Maybe it's for the best that they don't strictly enforce the characters ethnicity. Some examples aren't so good, like Storm, but then you have stuff like The Walking Dead. The lead actor is very british but you wouldn't know it from just watching the show. If they would've went for only american actors they might've picked someone bad for the role.
Hugh Jackman doesn't sound Canadian, he sounds like he's unable to hide his aussie accent. You're right about Prof X/Patrick Stewart not being French, I was thinking of his character in Star Trek. I should've known better, he was born to play that role.
How about one of the most ridiculous examples of changing the characters race?
John Wayne as Genghis Khan. It's so bad I can't even bring myself to watch it.
@Sora- I was just asking if you'd seen that because I think it's great and very faithfully done.