Okay, so to sum it up:
There is nothing wrong with carrying a full metal airsoft firearm in broad daylight as long as it's not out in the open, and secured safely in a case. If in case an officer stops you and asks for permission to look in the case, cooperate to increase your chances of simply being released and on your way. If for any reason, the officer gets on your case of you owning a non-clear airsoft firearm, simply tell him that you bought the firearm/firearm parts on Canada grounds.
Owning/transporting a full metal airsoft firearm in a case is legal, however importing certain metal parts such as barrels and/or receiver across the border is not legal. Leave importing of metal parts to the airsoft retailers located in Canada, and buy from them.
Did I miss anything?