Barcelona is in disarray so I'm tipping on PSG to go through. But since Barcelona's playing at home, I kinda feel they will not lose today. PSG will be looking for that away goal though so I think BTTS is a good option here.
I beg to differ. Barcelona looks much more promising right now when compared to PSG. Barca surely have edge over PSG in forward and midfield departments. Defense is where Barca failed to convince so far. However, Pique was solid in the few matches he played at the start of the season, he is back and most probably will start on the right side of CB pairing today. If Araujo isn't injured then him and Pique would have been perfect pair. But since he isn't playing, I think PSG would be able to sink in one goal, however, Barca will dominate the match and most probably win both legs. Neymar and Di Maria will be big miss for PSG.
@Trofo suggested me to go for BTTS bet on every match tonight, it's weird but bold suggestion so will give it a try as parlay.
Barcelona have been great in La Liga recently and I wouldn't like them to be very bad against PSG in the Champions League. Although Messi is having big problems with the club, he is still playing very good and helps his team to get decent results. For the first match, I can say that I'm waiting for Barcelona to win it. 
A lot depends on the result of the first match, and it is clear that Messi and the company understand this and at least will not lose this match. But everything is determined only by the match itself, and then all the layouts will be approximately clear. Also, let's not forget that the Champions League is a separate tournament and many teams can be transformed into both bad and good sides.