This doesn't happen often: Jesse Levine has decided to play for Canada. He was born in Ontario and moved to the US as a teen. Although he's currently ranked 104th in the world, he was ranked as high as 69th earlier this year. I remember him well from the US Open because he made it to the third round in September.
Here's more:
http://www.ctvnews.ca/sports/america...nada-1.1084752