City must not underestimate Copenhagen. But what we need to know is that Copenhagen experienced a difficult time in the group stage and they qualified for the next round after they surprisingly beat Galatasaray with a goal scored by Lukas Lerager and in the 1st leg Lerager couldn't play because of a red card. So I think it will be an easy win for City.
City certainly won't underestimate Copenhagen because this is the Champions League so just one defeat will have a big impact on a team.
I'm very sure about city not trying to underestimate Copenhagen even if they know too well that they are very likely to win Copenhagen without much stress, guardiola usually have got a very different approach with which he handles the champions league, so he will definitely not leave this for Copenhagen.
I'm the group stage Bayern Munich is the team that could be likened to city here in the round of sixteen against Copenhagen so comparing their performance against Bayern Munich in the group stage where they met twice we can tell to a great extent how much they can perform against city because city is even more experienced than Bayern Munich. I'm sure Copenhagen will have it tough with this one because city is definitely not going to make it easy for them in both home and away meetings, this may end Copenhagen champions league journey this season.