I expect Fed to not play Montreal (as it is the week after Olympics) and possibly Paris this year. Shanghai is a doubt too, and right now so is Rome (which I dont expect him to win anyway).
So realistically, I can see Roger winning only Cincinnati maybe. The surface suits him great anyway
As for Nadal, he is the favourite for Rome, he has had a fair bit of success in Montreal too in the past. However, given how he has performed at the Masters outside clay (ie: he has been very beatable at the final stages) in the last 2 years, its likely he too win realistically sit on 21 too.
But by the time both end their career, Nadal should have this record. He will be sitting on like 12 MCs by then for sure