Westjet does not fly to either Asia or Europe. Westjet does fly international (US, Mexico, Caribbean), but not intercontinental.

AFAIK Westjet does not place its code on other carriers' flights to Asia/Europe.

What Westjet does now have is interline agreements. If you want to fly to Asia/Europe, you can fly Westjet domestically/transborder and connect to certain international airlines (which will fly you over the Atlantic/Pacific oceans) on a single ticket. This will need to be booked via a travel agent or online source such as Expedia as to my knowledge the Westjet website only offers tickets to destinations served by its own operated/marketed flights.

Bottom line, I don't think there is any way that you'll be able to use your international companion ticket for Asia or Europe.