If Djokovic or Federer win Us Open they are the favorities for number 1.
I think there are a lot of variables in either scenario. In the ATP race, Nadal is at
5,760 points, Federer is at
4,020 points, and Djokovic is at
3,355 points.
1. if Federer and Nadal get equal points in Canada/Cincinnati and Federer beats Nadal in the U.S. Open final, Nadal has a 940 point lead after the U.S. Open;
2. If Federer and Nadal get equal points in Canada/Cincinnati and Federer wins the U.S. Open, with Nadal losing in the QF, Nadal only has a 100 point lead after the U.S. Open;
3. If Djokovic and Nadal get equal points in Canada/Cincinnati and Djokovic beats Nadal in the U.S. Open final, Nadal has a 1,605 point lead after the U.S. Open;
4. If Djokovic and Nadal get equal points in Canada/Cincinnati and Djokovic wins the U.S. Open, with Nadal losing in the QF, Nadal has a 765 point lead after the U.S. Open.
In #1 and #3, I favor Nadal for YE#1. In #2, I slightly favor Federer. #4 is kind of a toss-up between Djokovic and Nadal. Of course, it's entirely possible that a U.S. Open winning Federer or Djokovic gets more points in Canada/Cincinnati than Nadal or vice versa, and it's also possible that Nadal loses in the SF, R16, 3R, 2R, or 1R of the U.S. Open, all of which would impact the points.