If you're flying *A business class, you should be able to access the Maple Leaf Lounge in the International terminal. Don't know if the showers are open again yet.

https://www.aircanada.com/ca/en/aco/...unge@vancouver

You can also check out this thread for more info on the Maple Leaf Lounge:

https://flyertalk.com/forum/air-cana...iki-first.html

Also, I highly suggest you do not leave the airport - 5 hour connection isn't much time, given the potential for customs and security delays.