I can't really see Arsenal being able to defend Barca for 180 minutes. Chelsea and Man U have done it pretty well, but Arsenal have nowhere near their defensive discipline and Wenger will probaly not tell his boys to stay back. Really, I can't think of any part of the game Arsenal are superior in, especially if they are going into that match with Bendtner and Eduardo as their only strikers still.
Barca should beat Arsenal relatively comfortably, I'm just not a massive fan of both their styles of play. Much prefer direct, quick attacking football rather than slow intricate build up.