Knew this was a likely option as he has done that in prevous years. Interesting that Federer hasn't ever won the Montreal edition of this tournament.
It will likely serve Federer well for his fitness for the US Open, it makes the #2 seed at US Open more interesting though. Murray is just under 600 points behind Federer in the "Race to US Open" points right now. With Federer only playing Cincinnati he really needs to win or reach the final to have a good chance of keeping #2, and even if he wins it is quite possible for Murray to overtake him anyway.