You must have a particularly dim seller. Canadians buy from US sellers more than from Canadian ones. There should be no difficulty.
He goes to the USPS website. That will give him the services available to him. Suggest that he choose First Class International since that gives him Confirmation of Delivery and carries up to four pounds of product.
He enters the dimensions of the parcel and the weight.
The website tells him how much postage will be.
He invoices you with the selling price plus the postage.
You pay.
He puts either a Paypal shipping label (simplest) or postage on the parcel and takes it to his Post Office. (Americans can't just drop parcels into corner post boxes.)
USPS carries it to Canada and Canada Post carries it to you.
