We have inquired with ShipStation if it is possible to have both Canada Post and USPS/Stamps.com in a singular Shopify website that caters to both Canada and USA orders/customers. Unfortunately, this is NOT available. Currently, their carrier integrations are specific to account 'home country'.
As an alternative, we could at least have 1 Shopify website is to 2 or more ShipStation accounts. This is a temporary alternative (bandaid solution) but would have been greater if ShipSation is able to allow more global carriers in one Shopify account in view of both the app optimization and process efficiency. Because we're Canadian, proximity- and logistically- speaking, we can most definitely send out orders/packages outside of usual Canada Post and UPS options via another 3rd party provider.
Nonetheless, the alternative option is a relief! Just looking forward to the availability of these carrier integrations settings. Hoping this is of help! Thx