I'm unsure if Man City would beat Barcelona mainly because defensively they can be all over the place, positioning wise only Kompany and Zabaleta know how to defend, I still don't get why M.Richards gets so much of a love in when quite clearly going backwards he can be pulled apart. I remember when full backs were told to defend first.
Barcelona are lacking a finisher, a in the box striker that they have in Villa. In close games they need someone who only needs a chance. Barcelona missed 3 open goals against Chelsea and hit the woodwork twice. Crazy stuff. If one of those chances fell to Villa he would have buried it.
Also I think the signing of Cesc has disrupted their rhythm. They don't play as fluently as they did last season, Cesc doesn't really have a role in the team he just floats about. To beat Barcelona you have to defend deep, Inter Milan did it the best a couple of years ago - (Though Barca didn't get the calls they should have, 2 penalties, a disallowed goal for a handball that didn't happen, and suffered an offside goal - Probably karma from the Chelsea game the season before) but Inter in the first leg picked them apart on the counter attack as they had the pace of Maicon and Eto'o and the finishing of Milito. They also had defenders who knew how to defend for their lives. This is how you beat possession style teams like Barcelona and Arsenal of old.