The contenders will spend today trying to sway MPs, thought to include Shane Jones, Parekura Horomia and Andrew Little, who have yet to make up their minds. Mr Shearer and Mr Cunliffe have signalled the importance of a break from the Helen Clark-led years and have indicated a new look for the front bench of nine MPs.
They said speculation on the front bench was premature, but Mr Cunliffe said he would want Mr Shearer there, and Mr Robertson would also likely be there.
Mr Shearer said he had not given any undertakings to his colleagues.
A front bench that included all four contenders would ensure a step towards reconciliation after the leadership contest.
Adding MPs Jacinda Ardern, Mr Jones and Charles Chauvel, who was previously on the cross-bench, would see an injection of youth, policy gurus and the party's best performers in the House. David Parker is expected to keep his spot on the front bench.
Labour puts a lot of value on gender balance, and a front bench seat for Lianne Dalziel could be a reward for winning Christchurch East when most of the Canterbury area went to National.
She also showed courage by removing herself from the list. That would see a front bench that included two from the Maori caucus, two from the rainbow caucus and a mix of experience and youth.
Departing leadership team Phil Goff and Annette King are expected to vacate the front bench, as are Parliamentary veterans Trevor Mallard, Ruth Dyson and Mr Horomia.
Senior MP Clayton Cosgrove could keep his place on the front bench, but the new leadership team would be wary of being seen to reward him after he narrowly lost his Waimakariri seat.
The party will also elect new whips tomorrow, as former whips Rick Barker and Steve Chadwick were not re-elected to Parliament.
The whip position could be a reward for Chris Hipkins, who increased his majority in Rimutaka from 753 to 3286.
What Labour's new front bench could look like (in alphabetical order):
Jacinda Ardern
Charles Chauvel
David Cunliffe (right)
Lianne Dalziel
Shane Jones
Nanaia Mahuta
David Parker
Grant Robertson
David Shearer (left)