Wenger is obviously not mad enough to battle us for possession, but it will be interesting to see how deep he allows his team to sit and with what amount of pressure in different situations. One thing that is not brought up enough is the dynamic that Luis Suarez has brought to Barcelona. In years past, post Eto'o days, on some occasions teams could get away with packing their CB's tight and forcing us to beat them from the outside-in. It was pretty standard actually, especially the post-Pep days. With Suarez, thats no longer possible, his movement forces CB's to pick him up earlier than they would like to, and when you add in his unselfish nature to find teammates (ahem, Messi/Neymar), it makes our attack virtually unstoppable, especially for a team like Arsenal, who I wouldn't call a top defense.
For Arsenal to win or get a decent result, one of two things will need to happen.
1. They will need to get an early goal to allow their midfield to come behind the ball all while their forwards maintain the balance of tracking back and pushing tempo.
2. Their backline and Cech play the game of their absolute life.
Arsenal obviously have talent to execute the above (especially 1), but if none of the above happens, the match will go exactly like the game from the Etihad last year against Man City and Barcelona will leave with a win.