Amazon will not ship the "License Plate Adapter Kit for Subaru" to Canada. However, there are package forwarding companies that will provide a U.S. address to Canadians. You can buy from Amazon and have it shipped to a package forwarding company. The company then forwards your Amazon order to your address in Canada.
To find these package forwarding companies. Just search for terms like “package consolidation service” or “package forwarding”. There are lots of them out there.