Personally, I would exclude Bayern Munich from the list of the main favorites for now, too, leaving only Manchester City as the main contender for the Champions League title.
It means we only have a single candidate for UCL champion, right?
No doubt Man City is the strongest candidate, their quality is above other teams. Man City still showed good performance with no much different on their squad from the previous season. I think it is one of the reason why they have no problem with the cohesiveness in playing.
Nevertheless, the matches with Bayern with Bayer Leverkusen and Manchester United showed that the Bavarian machine is not yet so strong as to calmly grind any opponent.
If we consider the match against Man United, the problem of Bayern Munich is in the defense line. Bayern attackers have showed their best by scoring 4 goals. Unfortunately, Bayern Munich has weak defense, they got 3 conceded goals in second half. So, if Bayern Munich can solve the defense problem, they can be quite strong to be another candidate for the champion.
However, it is only the beginning of the season and there are no far-reaching conclusions based on these results., including on the basis of only the first round of the Champions League. More or less real layouts will begin to appear only in a few months in the middle of the season.
Sure, it is still the early of the competition. To know which teams that have good chance to reach the final UCL, it should reach the middle of the competition at least. So, it is still difficult to predict for the champion candidate now.