Customs wouldn't likely seize it (as far as I know). I've ordered a Tornado and PFI grenade and they were passed over during a customs inspection. Although, they CLEARLY look and feel like toys.
This is made of aluminum and could go either way. JAG Precision in the US is the North American distributor of Mad Bull products - so you can probably ask them.
www.AirsoftParts.ca,
www.Xtreme-Tactics.com/store, and (I think - correct me if I'm wrong)
www.CapitalAirsoft.com all carry a plethora of Mad Bull products in Canada. They should be your first point of contact for pricing.
Judging by the sound of it - you probably won't be able to use this in a gaming capacity however.