You can't arrest someone who is protected by diplomatic immunity. Cheney could walk down a Canadian street and shoot someone in full view of the public, and the most that Canada could LEGALLY do is to expel him.
Of course, you'd first have to prove that he actually was guilty. Something that no one in the US has been able to do. Sure,
www.lawyersagainstthewar.com have some "evidence", but something tells me that they aren't an impartial group.