I think it's too soon to make predictions for the three big clubs, we will never know the development of other clubs which may have surprises for the three clubs above, although I'm sure Manchester City will go smoothly to reach the UCL final this season but I think they should be able to overcome Copenhagen in the round of 16 because they also should not be underestimated. Every club that qualifies for the round of 16 is definitely not a club that is usually easy to beat. Manchester City will definitely have difficulties too.
I'm not sure that Madrid and Munich will run smoothly until the final, I think there will be a meeting between the three later, especially since Manchester City's meeting last season eliminated Munich and Madrid before the final, it looks quite good, it's just Madrid and Munich this season have talented new players who make it possible that there will be fierce competition if the meeting occurs again. I also hope that in the final Manchester City will meet Madrid or Munich.
But maybe that will happen again if they don't meet in the semi-finals or quarter-finals. I think there will probably be a big club meeting in the final. So far, these three clubs are the most favourites, but there are other clubs that cannot be ignored either.
Arsenal and Porto are in good form, same performance range, the probability is shaky, thesame with Napoli and Barcelona. For Madrid and Leipzig, one would say Madrid are in a better position to advance but the German side shouldn't be underrated though, they're also good in their own way. For Inter and Atletico, it's going to be a serious battle, none of them would allow the other to just go freely without making it tough. Hopefully these teams would use their home advantages wisely and to the best of their ability too.