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You sound very sure, and have must trust on City winning Real Madrid, which I don't think it will be easy for City to win Madrid. I cannot tell who qualify to the next round, but you should also consider that Real Madrid does not have home or away in UCL. They can win anywhere, so you saying they must make sure they win at home is somehow.
The two teams are very strong, and because City won last season does not mean that they have higher advantage over Real Madrid. You should also consider the change in players in Real Madrid squad, and I think that it is on that match day that we would know who is stronger. City was unable to win Liverpool, and they were praying for a draw in that match. Like you have forgotten that City is not as strong as last season.
We all never know for sure who will win the match until both teams finish the match. Real Madrid is strong, Manchester City is also strong and both have advantages which they hope to maximize throughout the match. But as a Real Madrid fan, of course I tend to hope that Real Madrid can progress smoothly to the next round by beating Manchester City this season.
The first leg will take place at the Santiago Bernabeu, so I think Real Madrid have a good chance of winning it. It is difficult to expect one of them to win, but the odds will certainly be more in favor of Real Madrid in the first leg.