I agree with those who think Yaya would be more effective further forward in this game, however I cannot see Pellegrini doing that right from the start.
Barca, given their "commanding" lead, will set out to play keep ball in the opening 20 minutes, and give City the run around and get those legs working overtime as early as possible, with the occasional burst here and there via Messi & Neymar etc. It's vital that City are still at 0-0 after 20 minutes or so. It's no use goin gung-ho from the off as, in all likeliness, you'll probably find yourself 1 down and that would be game over.
I know Clichy played on Sunday (and made a fuck-up), however I think you need his pace on the pitch from the start tonight, because Kolorov alongside Lescott lacks means there's a severe lack of pace down that side, to which Alves & Messi will be looking to exploit like they normally do. Of course there is a chance Pellegrini could opt for Clichy and Kolorov again.
I would imagine it would be something like this from the off:
Hart
Zabaleta-Kompany-Lescott-Clichy
Milner-Fernandinho-Yaya
Nasri-Silva
Aguero
More of a 4-3-2-1 just to cement your position in the game and to pretty much ensure you're still in with a chance after 20/30 minutes. Then I think Pellegrini will look at being a little more adventurous - try and push Yaya further forward so he's able to work in the same areas as Nasri & Silva, quick one touch passing, and always looking for the throughballs, and try and get Aguero running in behind or chasing some diagonals, because he's strong enough to hold the ball up against Barca's defense, and then he'll have Yaya, as well as Nasri & Silva, offering support.
Even if it's 0-0 at HT, that wouldn't be a bad situation to be in. Out for the 2nd half like this:
Hart
Zabaleta-Kompany-Lescott-Clichy
Milner-Fernandinho
Nasri-Yaya-Silva
Aguero
And then push the tempo and try to push Barca back if at all possible. Negredo & Navas would be the likely replacements, to inject some strength regards holding up the ball, and Navas to add pace. If Kolorov isn't on from the start, he'll certainly be an option should the outcome be in the balance purely for set pieces, as we know they are an achilles heel of Barca.
An early goal would make Barca sweat big time, however I really cannot see Pellegrini going for it from minute 1. Cement your position in the game and then build from there. Even if you take the lead in the 70th minute, Barca will shit themselves.
You don't have to try and level the tie by busting your bollocks from the first minute. They'll be aware of what City can bring in an attacking form whether it's the 10th minute or the 70th minute. You will get opportunites, and with Aguero on the pitch, you have someone who can take them no matter how rare they come.