I usually have to buy from the US as not many sz 13/14 (especially SBs) make it to Canadian retailers. But ya, parcel box in the US is a must - too many US retailers either don't ship up here, charge ridiculous ship rates ($40 - $50) or don't use USPS (FedEx/UPS/DHL all charge high brokerage fees, in order of best to worst in my experience). And some shoes don't make it up here (don't think any shop in Canada got the Baos for example).
Anytime I meet another Canadian that doesn't have a US parcel box, I have to assume (a) they don't drive/have a car, (b) extremely lazy, or (c) they have a criminal record.