Each parcel shipped by Canada Post needs to have a shipping label affixed to it. X-Cart's Canada Post add-on allows you to obtain shipping labels for your Canada Post parcels.
When creating a new shipment, the add-on contacts Canada Post and obtains a shipping label. You can access it using a link in the "Shipment info" section. Save the label you get as a PDF file, print it out, and affix it to the parcel.