Chelsea are in a very good form at the moment. If Chelsea face Barcelona or Bayern Munich then maybe the match will be a very strong match for Chelsea. But I think Chelsea will win. Chelsea are in a very good form at the moment. Every player of Chelsea is in a very good form. Although Barcelona or Bayern Munich are playing very well. But it is not possible to say for sure what will happen or not. Because both teams are very good and strong. And it is never possible to say when what will happen on the field of play.
As it currently stands about the performance of the teams you mentioned(Chelsea, Barca, and Bayern Munich), they are all in good form, from the front line to the defense line. No lapses in the squad depth. It will be hard for any of them to grab the 3 points of the match, if not much effort and tactics are put in the game to consider winning.
For winning, they got to play with all their might or expect a loss match which none of them, I believe would like to lose their match no matter who's the host or away team