Novak Djokovic defeated both Nadal and Federer this summer in Montreal, so I wouldn't rule him out.
2. S. Williams
Sharapova has a cakewalk draw. The the big guns on the women's side just happen to be in the same half of the draw, opposite Sharapova. V. Williams doesn't seem to play well anywhere outside Wimbledon these days, Serena hasn't played all summer, Sharapova withdrew from tournaments this summer with a shoulder injury. Justine Henin is looking to be the most prepared out of all of them, and just came off a win in Toronto. The problem for Henin is that she could face S. Williams in the QF
, and Serena for sure wants revenge after Henin defeated her in the QFs at both the French Open and Wimbledon this year.