I didn't realize this until I received my credit card bill. My reservation confirmation showed it was indeed US dollars. Usually I book round trip tickets, so this was a surprise to me. They had a discount promo on for US destinations. I could not get the discount on flights arriving in Lihue and then leaving from Honolulu. But when I checked one way flights I could get the discount and it was a decent savings.
I contacted West Jet and was told that online bookings from the US are done this way. I never would have expected being charged US prices from a Canadian Airline; so something to keep in mind when comparing Air Canada prices to West Jet.