It's a little confusing. Leaving aside the legal aspects (because I have no doubt about the full legality of these guns imported in Canada):
As they are marked .223, can they shoot 5.56 NATO as well? With what implications? Imediate safety concerns? Long term barrel deterioration? Accuracy issues? Or non of the above and "go for it, use with no problems .223 Rem or 5.56 NATO"?
Anyway, these are awesome guns at very good prices.