The wicketkeeper-batsman was yesterday named in a 19-strong squad which will be pruned to 15 in September.
Otago Cricket Association chief executive Ross Dykes said while McCullum had not confirmed he would play for Otago, he had exchanged text messages which indicated the gloveman was keen to front up for the Volts.
"As far as I'm concerned he is playing for us," Dykes said.
"It is not something Brendon would need to confirm. He qualifies for Otago and he is mad keen to play."
A tug of war looked as if it was emerging when the Sydney Morning Herald last month reported the New South Wales Blues were poised to offer a $US250,000 ($NZ45,000) transfer fee to secure McCullum's services.
However, Dykes said he had not been approached with any offer and he was confident McCullum would play for Otago.
England international Dimitri Mascarenhas was also named in the squad.
The hard-hitting all-rounder's Indian Premier League side, the Rajasthan Royals, failed to qualify for the Champions League, leaving him free to play for Otago.
Otago boasts a talented line-up which includes seven players with international experience.
Ian Butler, Nathan McCullum, Neil Broom, Aaron Redmond and Brendon McCullum were part of the Black Caps squad which contested the world twenty/20 tournament in England.
The squad also includes experienced medium pacer Warren McSkimming, promising opening bowler Neil Wagner and left-arm spinner Nick Beard.
Otago will begin preparations in early September.
Otago squad
For the Champions League
Neil Broom, Nick Beard, Derek de Boorder, Anthony Bullick, Ian Butler, Craig Cumming, Sean Eathorne, Shaun Haig, Mathew Harvie, Dimitri Mascarenhas, Brendon McCullum, Nathan McCullum, James McMillan, Warren McSkimming, Aaron Redmond, Hamish Rutherford, Will Somerville, Greg Todd, Neil Wagner.
