Along with the Chappell-Hadlee Trophy, one of the most illustrious careers in New Zealand cricket's history will come to an end as McCullum, their captain, will play his last game in the format.
Fittingly, the series is interestingly poised too with Australia bouncing back for a hard-fought win in the second ODI after succumbing to a massive loss in the first match in Auckland.
But despite the victory, Australia has concerns, especially in the batting department. It was skittled out for just 148 in 24.2 overs in the first game - the first time Australia failed to bat 25 overs - and was in trouble even in the second ODI before Mitchell Marsh and John Hastings bailed them out with a rearguard effort.
The World champions will, however, welcome the form of their openers - Usman Khawaja and David Warner. Khawaja returned to the format in the second game with a 50 while the ever reliable David Warner made a dazzling 98 before a middle-order collapse.
Australia's bowling has been a little expensive too, having conceded totals of 307 and 281 in the series so far. Josh Hazlewood, Hastings and Scott Boland form the pace attack while Adam Zampa, the legspinner, made a decent debut in the second game picking two wickets. Australia has also been hit by a back injury to Kane Richardson, who has been replaced by Joel Paris in the squad.
New Zealand's batsmen are in relatively better form but will want to convert their starts into big knocks. Martin Guptill has continued his impressive run, McCullum has given typically quick starts and the rest have chipped in too.
The host has an injury concern too, with Mitchell Santner picking up a foot injury in the second ODI. Santner has been in good all-round form too, making an unbeaten 45 and picking up three wickets in the game. New Zealand has called Ish Sodhi into the squad for the third ODI as a cover for Santner.
The series is on the line. A terrific career is about to end. New Zealand will want to win it for McCullum, but Australia is never known to show mercy. It's all set up for a fitting finale.
Australia: Steven Smith (capt), David Warner, Usman Khawaja, George Bailey, Glenn Maxwell, Mitchell Marsh, Matthew Wade (wk), Adam Zampa, John Hastings, Joel Paris, Josh Hazlewood.
New Zealand (from): Brendon McCullum (capt), Corey Anderson, Trent Boult, Doug Bracewell, Grant Elliott, Martin Guptill, Matt Henry, Adam Milne, Colin Munro, Henry Nicholls, Luke Ronchi (wk), Mitchell Santner, Ish Sodhi, Kane Williamson