Although Galatasaray and Bayan Munich are the best teams in their respective leagues, Bayan Munich will be avoided by many in terms of league qualification. There are many differences between Bayern Munich's playing eleven and Galatasaray's playing eleven. Bayern Munich are capable of beating any team in Europe but not Galatasaray. Everyone is considering Bayern Munich as the big favorites for the Champions League this season, if Galatasaray were a strong team like Bayern Munich or Manchester City, they would also be considered the favorites for the Champions League. Galatasaray may cause accidents in big matches but they will never be able to perform consistently against the big teams.
Galatasaray is always a tough opponent in the Champions League, despite not having a particularly strong squad compared to the others. It won't be an easy match for Bayern Munich when they have to play as guests at Galatasaray's stadium. Perhaps, Galatasaray will aim for a draw against Bayern.
Manchester united team will have to indeed win by all means and I know they would against Copahengen. For Galatasaray, the win may be harder than it would be, because the team is good and their passing accuracy across the pitch is intentional and full of a counter attack impact, if which Onana may not be ready to stop in time should the Manchester United defense remain porous.
The situation in Group A looks grim for Manchester United; they currently sit at the bottom of the table with 2 losses. They absolutely need to secure a win against Copenhagen, or their chances will be over. In my view, Onana shouldn't be featured in this crucial match.