Sixteen uncapped players were included Sunday in new coach
Back-rower Isi Naisarani and midfielder Tevita Kuridrani were the major omissions, and Rennie opted against any foreign-based players.
“When we picked the squad, we had to consider how we will handle the rigours of the Test calendar ahead,” said Rennie.
“It is obviously a big squad which is due to Covid restrictions as we can’t bring players in and out but each of one them is there on merit.”
He already has some injury problems after a bruising Super Rugby AU playoff game on Saturday between the Reds and Rebels.
Hooker Jordan Uelese appears to be the biggest worry after leaving the field with what looked like a shoulder injury.
His Rebels captain Dane Haylett-Petty also limped off, with playmaker Toomua and Reds’ outside back Jordan Petaia joining the walking wounded.
The four-nation Rugby Championship is due to be played in Australia between 7 November and 12 December, after governing body SANZAAR opted against early frontrunners New Zealand as host.
Australian quarantine regulations were considered more relaxed, with teams able to train together in large groups while in mandatory 14-day isolation.
This was important given neither South Africa nor Argentina have resumed competitive rugby since the pandemic brought sport to a halt earlier this year.
To compensate, the All Blacks’ two Bledisloe Cup Tests against the Wallabies, due to be played in Australia, will now be in New Zealand. Dates have not been confirmed, but 17 and 24 October appear most likely.
Australia squad: Jermaine Ainsley, Allan Alaalatoa, Tom Banks, Angus Bell, Filipo Daugunu, Pone Fa’amausili, Folau Fainga’a, Jake Gordon, Ned Hanigan, Will Harrison, Dane Haylett-Petty, Reece Hodge, Michael Hooper, Tom Horton, Trevor Hosea, Len Ikitau, Harry Johnson-Holmes, Marika Korobiete, Noah Lolesio, Jack Maddocks, Tate McDermott, Fraser McReight, James O’Connor, Brandon Paenga-Amosa, Hunter Paisami, Jordan Petaia, Matt Philip, Joe Powell, James Ramm, Lukhan Salakaia-Loto, Pete Samu, Rob Simmons, Irae Simone, Scott Sio, James Slipper, Lachie Swinton, Matt Toomua, Taniela Tupou, Jordan Uelese, Rob Valetini, Nic White, Harry Wilson, Liam Wright, Tom Wright