My money is on Dzeko lining up behind Aguero. They love their 4-2-3-1 and don't seem likely to change it, no matter what happens.
Frankly, I think the United 4-2-2-2 would work brilliantly for them, as well as in the EPL, and ensure them being a competitive squad. As mentioned, the EPL is a very wide league, with the need for defensive fullbacks significantly increased.
While £35M is a lot, for a player with Aguero's abilities and work rate, they might have underpaid.
If I was running City, I think a 4-3-1-2 is probably their best formation.
Hart
Richards Kompany Lescott Clichy
Milner Barry Toure
Silva
Aguero Dzeko
They can reasonably sell a lot of their forwards and beef up their midfield, which I still think is problematic.