PSG has Mbappe, Mbappe has the ability to score a lot of goals. On the other hand, Barcelona's Lewandowski is a very experienced player. Lewandowski has the ability to break down PSG's defence. So considering the squad I cannot consider a particular team as favourite.
PSG coach Luis Enrique is well aware of Barcelona's gameplay. He knows very well how Barcelona plays the game tactically. And I would say this is Barcelona's main weakness. Xavi will have to apply a different match strategy if he wants to beat PSG. Otherwise, Luis Enrique's side will not win Barcelona against PSG.
Luis Enrique who once managed Barcelona, is of course very well known about the way his former team played, he can more easily find tactics that can narrow down the movements of Barcelona players in developing their game. Mbappe is of course the key player that Luis Enrique will use to break down Barcelona defense, his ability to score goals cannot be doubted, he also has a strong physique and is able to run fast which can trouble Barcelona defense area.
However recently Barcelona's style of play has improved much more than before, the victory over Atletico Madrid indicates that they are ready to face PSG. The clubs that are still in the UCL are a little worried about the international break, the FIFA virus often attacks the players which makes them hit by injuries.