@swojnicz still a US entity cannot legally collect tax from Canadian client. Scenario is company A (Canadian company) sold a product to a US entity company B, which resold the product to a Canadian customer, in this case technically company A should not be charging any taxes, further more if company B charges taxes then the product gets double taxed. One option could be is to claim input tax credit from Canadian Tax agencies by company B if company A charged taxes. Work around would be to add the Canadian nexuses to your US sub along with the associated tax group and codes - this will allow you to collect taxes (still product gets double taxed). You got to ask CRA about your scenario https://www.canada.ca/en/revenue-agency/services/tax/businesses/topics/gst-hst-businesses/definitions-gst-hst.html