Yep.. USPS won't ship compressed air. As for why UPS over Fedex.. American's love UPS.. and use it more than the post office down there. FedX is rarely a choice with US companies for shipping.
We should have taken a group order... one large pallet across the border on a truck.. I could have cleared that, or an entire truck load for that matter, for only $55 with Near North Customs Brokers in Barrie!!