American, Canadian, what's the difference? Aren't we all just citizens of the world?
As to the question, due to some somewhat controversial rulings about Arioch/captured humans/captured prophets that have recently been brought up, I would say that currently, captured characters cannot be targeted as that nationality (i.e. discard an Assyrian doesn't allow you to discard a captured Rabshakeh) but cards that refer to there being a character of that nationality in play work (i.e. If a Babylonian is in play, do X cards would allow you to do X if a captured Nebby/Nergie is in play).
If it sounds inconsistent, well it is in my opinion. But that's just me.
