That's because the company doesn't schedule an inflight service on SEA-YVR. It's not as though the FA's just decided to forego a beverage service in favor of doing the Visa schpiel instead. Typically, on the SEA-YVR flight there is time to pass out the U.S. customs forms on board and by the time that's finished we are usually on descent. Personally, I don't do the Visa thing, and don't really enjoy it when other FA's do. That said, nobody ever foregoes a scheduled beverage service to hawk the Visa's.