There are different variations how you can play the three at the back in the 3-5-2 system.
offensiv minded = 1CB,2WB
"neutral" minded = 2CB,1WB (used by Pep in the past, Tuchels approach)
defensiv minded = 3 CB (Conte,Simeone,Ole)
Personally i would love to see Walker, 1CB, Cancelo at the back. I think 3 CB is counterproductive to how most of the teams will set-up against city.
It's Ederson at the back and the other 10 up front 1-10