Good points indeed, takao. I'm quite convinced that Barca passes Bayern rather easily. They haven't played them for a long time, so I guess that could boost a little their ambitions. But most of all, Bayern has to play without Kroos (and Mandjukic for the first game). Two crucial elements missing without proper replacement (not a Gomez fan over here).
IMHO for the Barca Game Müller in the central position is the better choice even if Kroos weren't injured
Kroos with his excellent through passes, agility, long shots, corners, free kicks etc. is excellent against defensive teams sitting deep but against an offensive team Müllers qualities (pace, work rate, defensive discipline, running into space on the counter)
It could also very well happen that Mascherano has to play as a central defender in the Barca line up. He is perhaps one of the best tacklers in the game but he is a rather ill fit against a classical centre forward like Gomez or Pizarro, especially on the counter. And he has hardly good memories playing against Müller either...
both teams wing backs defensive abilties will also be put up to the test as well ... Alves is brilliant on the attack but him playing defensivly against Ribery ? i would put my money on a yellow card for him within 15 minutes
for comedy relief i now present Bayern's back four from 2009 when they lost 4:0 to Barca: Oddo, Demichelis, Breno, Lell
BVB-Real is almost 50/50 I'd say, Dortmund loves being the underdog. I'm quite tempted to get a Sky receiver right now
Dortmund simply lacks any good players on the bench: Julian Schieber as the striker back up 'option' can only be considered a joke
Sure in the centre midfield they can mix it up with Gündogan, Bender, Kehl & Sahin but offensive he has zero choice