Nole is a heavy favorite for AO. I don't really see Fed beat him there. Murray could, but it will be though.
If Nadal is not in good form for Roland-Garros, then Fed will give it a real shot, which I don't think he did in 2012. They are 3-3 on clay, 1-1 at RG. Nole would be a favorite, but it wouldn't be a given for him to beat Fed. Del Potro could also be a threat in Paris.
Nole won't be favorite at Wimby if Fed and Murray are in good form. Other player could beat him in a good day (Tsonga and Berdych).
The US Open is...open. It Murray, Federer, maybe Del Potro can beat him here.