In Canada, we generally ship only to street addresses, not post office boxes or Rural Route numbers used exclusively by Canada Post. If an order is submitted using a PO Box or RR number only (with no deliverable street address), the shipment may be re-routed to the closest courier depot or agency, if Canada Post shipping is not available for that shipment. That courier office/agent will then contact the customer for pick-up of the item.
In the US, items that are able to be shipped via the United States Postal service can be delivered to any US Post Office box or rural route. For items that, because of their size or weight, must ship by other carriers, PO Box or Rural Route addresses are not valid.