Canadian government imposes an anti-dumping duty on certain products.
Its great that they gave you heads up. Yup, this is the stuff that drives us and them nuts. My last order from them (many years ago before they decided to high grade accounts to commercial/education) was a stack of customs paperwork. A stupid bag of small metric fasteners incurred this rate, the next size up did not or a different rate based on material, source country, quantity. Its that processing that costs them money. Thank out government(s) for this mess. I can understand big trade issues like oil, lumber, metals. But 20$ worth of screws? Its not like hobbyists are going to ever tip the scales of international trade. The sad thing is, the same thing from Ali or Ebay, flies right in with minimal fuss.