David Warner and Will Pucovski have returned in the Test Squad but Joe Burns, who played the first Two Test, has been dropped for the third Test against India in Sydney. Both the openers have been in the squad earlier but were ruled out because of their respective injury.
Joe Burns has been dropped because he has managed to score just 8, 51*, 0 and 4 in the opening two Tests in Adelaide and Melbourne respectively. His form has been under question ahead of the start of the series but the unbeaten half-century gave him another opportunity to play in the second Test. But Burns could not prove his case. Notably, it is the sixth time he has been dropped from the Test career since his Test debut six years ago.
David Warner Practising In Nets:

As far as David Warner’s groin injury is concerned, the left-hand batsman has been seen practising in the nets and running a bit, showing improvement. But it is still not confirmed that he will be playing the third Test in Sydney.
Talking about the youngster Will Pucovski, he was ruled out after suffering the ninth concussion of his career during the warm-up game against India A. But the selectors have said that the young gun has been symptom-free for some time now. And, he can likely make the debut in Sydney.

But if he opens with David Warner, Matthew Wade, who played as an opener in the first two, might be dropped or demoted to middle-order.
Meanwhile, currently, the four-match Test series is even-steven with India making comeback in the second Test in Melbourne. The all-important third Test will begin on January 7.
Australia Test squad: Tim Paine (c), Sean Abbott, Pat Cummins, Cameron Green, Marcus Harris, Josh Hazlewood, Travis Head, Moises Henriques, Marnus Labuschagne, Nathan Lyon, Michael Neser, James Pattinson, Will Pucovski, Steve Smith, Mitchell Starc, Mitchell Swepson, Matthew Wade, David Warner