While Australia is already assured of appearing at the 2019 showpiece event in England, the five-match series against England beginning at the MCG on Sunday offers plenty to play for individually, for this is the time when the national selectors sharpen their culling process.

Selection chairman Trevor Hohns knows all about this, having overseen Australia's winning World Cup campaigns of 1999 and 2003.

This included ending the one-day careers of Test greats Ian Healy and Mark Taylor a year after losing the 1996 World Cup final to Sri Lanka, and dumping Mark and Steve Waugh a year out from the 2003 World Cup in South Africa. In Mark Waugh's case, Matthew Hayden and Adam Gilchrist were confirmed as the new opening partnership, while Steve was not only axed as captain but from the team.

Ricky Ponting was made captain and a refreshed unit, free of the controversial rotation policy of that time, would charge unbeaten through the '03 World Cup and again in '07, when Andrew Hilditch had replaced Hohns as chairman.

More than a decade on, the selectors, with Hohns back at the helm, have been praised for making the right calls this Ashes summer - and hope to replicate those heading into the 2019 World Cup defence.

Fairfax Media understands the selectors do not yet believe they have assembled a big enough core group of players, and this remains a major focus.

Hohns, in Melbourne this week, already has not been afraid to deliver a statement to Glenn Maxwell by controversially dropping him and recalling Cameron White for his first match since 2015.

Maxwell, the leading run-scorer in the Sheffield Shield, was put on standby for the Ashes opener in Brisbane but there are suspicions his axing from the ODI squad has just as much to do with form in the 50 overs format - having averaged 22 in his past 20 matches - as it has off-field issues. Smith wants him to train smarter - that is, become a more conventional batsman - while the whispering campaign about how well he gets on with teammates, along with other issues, have been bubbling through cricketing circles.

Maxwell was part of the winning 2015 campaign, one that already has had four definite changes after the retirements of Michael Clarke, Shane Watson, Brad Haddin and Mitchell Johnson. James Faulkner, like Maxwell, has lost his spot, with Marcus Stoinis and Mitch Marsh the preferred all-rounders.

Peter Handscomb was a part of Australia's last one-day series campaign, in India, but also finds himself on the outer after a year where the national side won only five of 15 completed one-day matches - four against Pakistan.

There were 25 players used last year, in part because of injury, form and experimentation, while six were rotated through the crucial No.4 spot - a position traditionally reserved for the best batsman. The time is right for Travis Head, who played in every match ODI last year, or White to seize that prize.

Head, given that responsibility in the 4-1 series loss to India in September, failed to deliver a half-century in all five matches but will have first bite against England.

"The middle order is probably where we have had a bit of an issue. Guys up the top have been scoring some big runs, Davey [Warner] has been exceptional in one-day cricket for the last couple of years. Finchy [Aaron Finch] played very well in our last series in India so our middle order is a key area for us to focus on," Smith said.

"We need runs out of that middle order, in particular wickets in hand to have an onslaught at the back end of the game, something that we haven't done."

The frontline pace attack of Mitch Starc, Josh Hazlewood and Pat Cummins is set but it remains a guessing game as to who will be the back-up quicks come England. Nathan Coulter-Nile, the leading wicket-taker in the Indian series (10), would appear to be No.4 when fit but his career is in limbo because of stress fractures in his lower back.

Kane Richardson, Billy Stanlake and John Hastings were all given a go last year - now West Australian pacemen Andrew Tye and Jhye Richardson have a chance to debut.

Another debate is who will get the job behind the stumps. Matthew Wade was seen to be the man but his ODI form with the bat against India, compounding his troubles in Test cricket, gave selectors no other option but to drop him. He managed only 34 runs at 11.3, and was replaced by Handscomb in one match. He had only the one innings in the Champions Trophy in England (two runs) last year.

It's been a stunning rise for Paine, who had all but given up hope of even a regular first-class match this time last year. Paine's 26th - and last - ODI was against Bangladesh in Dhaka in 2011. He averaged just under 30, with a century against England in Nottingham in 2009.

Should the 30-year-old continue to average a similar figure, he will be safe. But there is the intriguing option of Handscomb taking the gloves - as he does for the Melbourne Stars in the BBL. Handscomb has averaged a modest 21.28 in eight ODIs - he is a far better player than that - and, at 26, could be the best long-term option should he spend more time honing one of the game's toughest crafts.

Selectors also remain keen on Chris Lynn, despite another injury setback, and believe he could emerge as part of the core. The Queenslander is seen as the hard-hitting slugger capable of clearing the pickets on the small English grounds. The issue is whether he can stay healthy, for neck, shoulder, hamstring and calf issues have cruelled his past year.

Finch said there was still time for experimentation in a bid to find the group the selectors are craving.

"You look at guys who are bankers in the side - Smith obviously, Starc, Cummins Hazlewood, Davey Warner - that no doubt will be in the future but I think there is probably a chance to tinker with a few things and try and make sure we get our balance right," he said.

Aside from selection, game style and tactics must be solidified. The Australians crashed out of the rain-marred Champions Trophy - defeat to the host nation due largely to a Ben Stokes century, the final frustration. Then came a 4-1 series defeat in India, leaving Smith's side at No.3 in the world rankings.

As Smith said, the regular loss of back-to-back wickets has hurt, particularly in the middle overs, but Finch and Warner will maintain their blueprint of attacking in the first 10 overs to kickstart Australia's innings.

The ICC's Future Tours Program is a fluid - and unclear - beast but Australia have about 28 one-day internationals left before the World Cup. As Hohns said, the sooner Australia "can settle on our best combination and get them playing together and in form on a regular basis then the better our chances will be of retaining the trophy we won at home in 2015".

One-Day International Series against England

MCG: January 14

Gabba: January 19

SCG: January 21

Adelaide: January 26

Perth: January 28

Australian ODI squad v England

Who will be part of the 2019 World Cup defence?

Steve Smith (c)

Averaging 43.23 with eight centuries. Will lead the team to England next year.

David Warner (vc)

Arguably the world's best ODI batsman, averaging 44.94 and a strike rate of 96.58. Will be in England.

Pat Cummins

Has 57 wickets at 29.24 in 36 ODIs and will be part of a three-man pace attack - fitness permitting.

Aaron Finch

Has solidified his spot at the top of the order, averaging 36.56, with eight tons, and should be there next year.

Josh Hazlewood

Has 64 wickets at 23.85 in 38 ODIs and will be one of Australia's key weapons.

Travis Head

Can bat anywhere in the top and middle order and provides handy off-spin. Expected to be in England.

Cameron White

At 34, the former T20 captain has been given the chance to resurrect his ODI career. Strong chance now for England.

Mitchell Marsh

Is averaging 35.48 with the bat and has 41 wickets at 36.17 in 48 ODIs. Selectors hope he will be a middle-order rock.

Tim Paine

At 33, has replaced Matthew Wade behind the stumps in a sign he is seen as the right fit for the next 18 months.

Jhye Richardson

An emerging fast bowler who made his international debut in the T20s v Sri Lanka this year. One to watch.

Mitchell Starc

Will spearhead the attack at the World Cup, with fitness chiefs to keep a close eye on him leading into a World Cup and Ashes in England.

Marcus Stoinis

Made his ODI debut at Leeds in 2015 and is seen as a batting all-rounder who could flourish in England.

Andrew Tye

One of the stars of the BBL, Tye has played seven T20 internationals but yet to make his ODI debut.

Adam Zampa

Doesn't turn his leggie prodigiously but has variation and has become the team's frontline spinner. Should make it to England.