May is a lifetime away but as it stands now: You need to be fully vaxed more than 14 days prior to the trip. Create an account in ArriveCan. Within 72 hours of your trip, add your flight info and upload proof of vaccination. You will need either a molecular test (PCR, NAAT, LAMP etc) taken within 72 hours of the departure time of your SEA-YVR flight or an antigen test taken the day before that flight or a positive molecular test result taken within the previous 180 days.