Finch says: "It looks a good wicket; if there's anything there it will be early on."
Finch named an unchanged lineup but said power batsman Chris Lynn would likely be moved up to open.
South Africa, which also named an unchanged side, won the first match in Perth by six wickets and Australia the second in Adelaide by seven runs, ending a seven-match ODI losing streak.
Lineups:
Australia: Aaron Finch (captain), Travis Head, Shaun Marsh, Chris Lynn, Alex Carey, Glenn Maxwell, Marcus Stoins, Pat Cummins, Mitchell Starc, Adam Zampa, Josh Hazlewood.
South Africa: Quinton de Kock, Aiden Markram, Reeza Hendricks, Faf du Plessis (captain), Heinrich Klaasen, David Miller, Dwaine Pretorius, Dale Steyn, Kagiso Rabada, Lungi Ngidi, Imran Tahir.
Umpires: Paul Wilson, Australia, and Aleem Dar, Pakistan.
TV Umpire: Michael Gough, England. Match Referee: Jeff Crowe, New Zealand.