Which team wins will depend on the performance on the field, but given the way Manchester City and Real Madrid are currently performing against other opponents, I'm slightly ahead of Manchester City in this match.
That's surprising. If we're talking about form isn't Madrid better? At the time of writing City plays in the FA Cup and the score is currently 2-1 for City, which is quite subpar considering the opponent and their line-up for this match. Not to mention their last defeat against Arsenal shows how weak they are with ball retention and pass accuracy. If Madrid plays a counterattack and press high I believe they'll have a lot of chances to score if City fails to solve those problems until then. CMIIW.
Guardiola is a coach who will not just sit back and watch his team slump, especially when the news about City losing 5:1 to Arsenal is still going viral. Guardiola must be thinking of a big plan to create a surprise and if we talk about Madrid, then City is a tough opponent, even in their last 5 matches, City won 2x - Madrid 1x - drew 2x.
the conclusion I can draw is that the strength of both is very balanced imo.