And I know what you're thinking:
1. Alphonso Davies is quick enough to negate the Mbappe factor
2. Bayern can adjust their playing style in anticipation of the Mbappe threat
Here's why that won't work
Alphonso Davies and Kylian Mbappe both line-up on the left side for their teams, which means they'll actually be on opposite sides of the pitch. Mbappe will likely come against the combination of either Kimmich/Pavard at right-back paired up with Jerome Boateng at center back. As world-class as Boateng is at reading the game, he struggles as aa 1on1 defender due to his lack of pace.
The game Bayern lost 5-1 early in the season, to a Frankfurt team that finished the season in 9th and got the previous Bayern manager fired, was kicked off by a Boateng red card in the 9th minute after he was left 1-on-1. The second goal Barcelona scored in the quarter-final was from a mistake in 1-on-1 defending by Boateng. If PSG can get Boateng isolated throughout the game by exposing the high line, Bayern is going to have a very tough day.
Niklas Sule is an option, but he might be an even worse matchup versus Mbappe. You could slide Alaba slides over to the right-center back, but that limits what he offers the team playing out of the back on his preferred left foot.