Here's an article on Levine from the Montreal Gazette:
It discusses his decision to play for the U.S, which was discussed here a while back. He doesn't completely slam the door on playing for Canada in the future, but it sounds pretty unlikely. "I'm not Canadian. I hate when people say I'm Canadian. I play for the U.S.," he said.
It's funny he says that because the commentator during his match at the U.S. Open kept referring to him as Canadian. It was probably an honest mistake, but I get the impression that some fans and members of the media think of foreign-born players as being less American.
BTW, the author of the article said that Levine can represent the U.S. because his dad is American. Correct me if I'm wrong, but isn't that irrelevant to whether he can represent the U.S.? All you have to be is a citizen, right? I know that foreign-born Americans like Nikita Kryvonos and Alex Kuznetsov have been Davis Cup practice partners, and I don't think their parents are American-born.