I just ordered these. Not sure what they charge to ship to Canada but given the initial low price for the filters, might still be cheaper than ordering elsewhere.
https://www.filterheads.com/i-642-a...dia-3pk-buy-2-get-1-free.html?ref=category:12
Edit: Just checked the FAQ on their site, shipping is also FREE to Canada.
Q: Does FilterHeads sell to Canadian customers?
Yes, and shipping is also free for them. We ship to Canadian customers via USPS. All duties and Canadian taxes are the responsibility of the customer.