U can wangle the EU software to work on US servers, but you cannot use a EU cdkey to create an account on US servers.
I wouldn't recommend Using EU software on US tho, lots of people who do are getting all sorts of issues with the latest patches...
While I perfectly understand why you would want a collectors edition of such an awesome game as WoW, your life will definitely be easier just getting a CD key from someone like squish102 and source the software from a friend.