Bayern will have the possession, but then it gets tricky.
When you play bayern, you need to keep their defence deep by having a strong and fast forward stretching them, and worldclass midfielders who win duels and can recover possession.
Otherwise, they will move their defence very high, and you'll get shafted by that movement in the box.
Bayern is excellent at isolating your frontline. They also have vidal hunting down midfield runners when you do actually counter.
Barcelona does not have the players to combat their midfield. Bayern, when everyone is fit, does have the defenders+Vidal to play very high and isolate their forwards.
If barcelona sits back, they wont be able to stop bayern, and they wont make most of the counters.
They are the one team that can take possession of barcelona, while isolating their forwards. And good luck for Messi to drop deeper and face vidal if he's sober.