Both teams played very well in the Champions League but if you look at the opponents I don't think it's tougher than Leverkusen because this club is facing clubs that usually compete in the Champions League so I think Leverkusen will beat Brest no matter what or at worst get a draw.
For the chances themselves Leverkusen has odds @1.50 as a club playing away I think that's a pretty good chance to bet on but we also need to be prepared if there is a surprise Brest itself has pretty high odds as a club playing at home that is @6.40.
To even start with, Brest isn't an experienced UCL team, in fact at some point, it feels like they were lucky to be able to make it to champions league this season because they are not a regular appearance at the champions league, and coming from a less competitive league is a disadvantage on their side already which Leverkusen may have settled from their own end even if they aren't better experienced in the UCL but they are on a very different level when compared to Brest, most likely I'm believing they will win this fixture.
I see Brest chances of winning this match as very small even though in the previous two games they managed to achieve two consecutive wins. The only reason I doubt Brest's quality is because they are inconsistent in maintaining their performance despite being in a less competitive League. Meanwhile, Leverkusen players are in full confidence after achieving an important victory over Frankfurt in the Bundesliga. The difference in level between the two teams allowed Leverkusen to dominate the match and achieve their third consecutive win in the UCL, especially since in the previous match they managed to achieve a crucial win over Milan.