He is Canadian by birth, but he calls himself an American in the ad. I don't think it's swaying any voters. People see through this kind of ad.
He's an opportunist who uses his nationality when it suits him. In this case, he's forsaken his nationality for the sake of influence, pure and simple. He's a good actor, an actor remember, who is using his skills and dialogue which may or may not be accurate to sway an election with which he has absolutely no 'dog in that hunt' (the particular election he's advertising for). I used to like him, but I don't any more.