Sales tax can be paid in any currency. The tax man does not care. It's all money.
Your seller is probably enrolled in the Global Shipping Program. Unless the item is over $50, eBay does not encourage sellers to use the GSP, but many do . It has been poorly explained.
The GSP shows as a note under the Shipping Cost that says something to the effect of Import Charges $X.xx. If you think the total cost is too high, don't bid.
The Import Charges consist of Canadian Duty, Canadian GST/HST/PST, and a small service/shipping charge that goes to PitneyBowes, who process the items for trans-shipment to Canada,
Many US companies who trade into Canada are authorized to collect and remit Canadian duty and taxes. UPS and FedEx do this every day, but they do it on your doorstep. There are older threads thousands of posts long screaming about this. LLBean is another that comes to mind.
