I've been here 6 years and I can't tell the Americans from the Canadians round here (unless the Canucks rather helpfully add the "eh" at the end). I can spot a Texan or a Californian, but I've got no chance with a Michigandan and our nearest neighbors over the border. Apparently they can tell, though.
But that's OK, 'cause most of them can't tell if I'm Aussie or Brit.