I'd go with the Challenger anyway. As mentioned, although its assembled in Canada it still supports what is largely an American company. Buying from a foreign automaker that assembles its cars here makes some sense too, but you're only looking at supporting the factory workers. The large part of the company is still overseas, and you'd better believe that's where the money goes.
And building cars in Canada isn't new. Hell, my 1971 Dodge Dart was assembled at the Windsor, Ontario plant. $30k would buy a REALLY nice A-body though. Just make sure you check the fender tag to make sure it wasn't a Windsor car!