Bayern has indeed lost quite a lot of its main players, not only Lewandowski who cannot play. There are 4 other main players who cannot play such as Costa, Gnabry, Sule and Tolisso. Meanwhile, PSG is likely to be strengthened by Florenzi and Verratti, who as you mentioned. Indeed, if you compare the line-up of PSG players it looks more prepared. Therefore, I am not surprised that you prefer PSG, who are favorites to qualify for the next round, but I did not change my decision by still choosing Bayern who will qualify for the next round.
And yet the bookmakers are still putting them as favorites as I can see,,, so being the away team and being without many key players they are still considered a strong unit to win. I would also still bet on BTTS on this one, maybe the game even ends up being a draw after all. PSG will want to draw as well or even lose by 1 goal and just keep the away goals advantage.
They put bayern as favorite for the second leg tonight but if you look at the odds on who will advance into the semifinal than you can see that PSG is the clear favorite here, which of course is no surprise given the result of the first leg.
I have to say though that i can easily imagine bayern to score 3 or 4 goals tonight because they have so much quality in the offense that they can score that amount of goals against pretty much every team. They need to be way more efficient than in the first leg with their goal scoring of course because that inefficiency brought them into this bad position in the first place.
Another main factor will be the quite shaky defense of bayern this season, but if they manage to only concede one goal at max than everything is possible.