Hi Mathew,
I am afraid I do not understand your use case.
For US customers ByDesign requires the tax jurisdiction of the customer in order to calculate taxes applicable in the US.
If your customer is located in Canada the system will most likely calculate taxes for Canada. Thus no tax jurisdiction is required.
If I understand you correctly even though you have a canadian customer the transaction is taxable in the US. If so the ship-to location would be in the US, right? Or am I missing something?
Best regards,
Stephan