Thank you for your replies. Now that I know metal bodies alone are a sketchy topic (and I don't want to get in unnecessary trouble with the law), how about this G&P "ProKit" that Evike USA has? http://www.evike.com/product_info.php?products_id=42014
It basically looks like an AEG without the stock and barrel, and comes with an M120 spring (which theoretically would be in excess of 366 FPS in an assembled AEG), so maybe they won't see it as a potential "real steel" firearm receiver; could there be any chance that this G&P "Pro Kit" could pass the CBSA?
I've sent Evike USA an e-mail about it, but I don't expect a response anytime soon.