If the concern is proof of purchase in Canada AND you do not have a receipt AND there is no record of the serial number at the import level, just go into any Canadian customs office (any airport, border crossing and maybe an office here and there).
Show them the product, record the serial number and description on the "green" form.
They will stamp that the item was presented in Canada thus all taxes have been paid.
That should work as proof of Canadian product for export/import without further taxes.
Peter, if you have contact with the Feds, see if that will be sufficient proof for future warranty shipments. It should be as it was fine when I fly into the US recently.
Jerry