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.
However, now many people believe more in Leverkusen to be able to win this match. That is something that is very natural considering that Leverkusen is a team that is in good condition this season, they also have a mission where they must be able to go further when they are in the Champions League this season. While Brest who will be their opponent in this match is actually not a very favored team, I don't even remember how many times they have been in the Champions League. However, Leverkusen should not underestimate this team, because if they underestimate Brest then maybe Brest will do something that can make them very surprised.