Honestly, I have no idea. Maybe this may explain the 5%:
https://www.canada.ca/en/revenue-age...s-exports.html
"Imports
Most goods imported into Canada are subject to the federal GST, which is calculated at the rate of 5% of the duty-paid value of the shipment. This tax must be paid at time of entry and is collected at the border, unless the goods are going directly to a bonded warehouse. In this case, the GST is collected when the goods leave the warehouse and become eligible for sale in Canada.
Several provinces have combined the GST with their provincial sales taxes on various categories of goods, thus creating a Harmonized Sales Tax (HST). On most commercial imports, however, only the federal (GST) portion of the HST is applied to the sale."