There isn't much to compare between these two teams. Bayern Munich will always be favourites to win, not because of their name, but because of their style of play and long-standing domination in the Champions League competition. Galatasaray may be good and doing very well in both their domestic league and the Champions League, but they have no chance against Bayern Munich no matter what even if Bayern Munich is in poor form and performing ineffectively. Bayern has already won the group stage, and we should be thinking about who they will face in the qualification round.
The game of Bayern Munich with Manchester United showed that the club is not perfect with the defense and 2 goals of MU is a vivid illustration of this. Galatasaray, too, under certain circumstances, can rest and achieve results, so you should not discount them and give an unconditional victory in advance. Bayern Munich has certain moments when the team gets lost and allows the opponent to get back into the game again.