The easiest way to transit between borders is via the NEXUS program. Make an appointment with
Customs & Immigration at Boeing Field,
Seattle (206) 553-0667. Ask what documents you will need, it seems to change year to year, for the interview. Once the interview is done you’ll move to the next office and interview with Canadian
Customs. You’ll then become a “Preferred Traveler” which allows you to clear in via
phone on your boat in either direction. Call customs when you are within the hour of crossing the border to receive the clearance number. Customs can still require you to report to a customs
dock but in all the years I’ve participated in the program I’ve never been asked to do so. Another benefit of being pre-qualified for crossing the border is international travel. Returning from
Mexico I landed in LA and used a kiosk to clear immigrations. You insert your passport into the reader and up pops your profile. You answer the usual questions on the touch
screen; upon completion it prints a receipt with your passport
photo. Show the receipt to the immigration officer who then waves you through. I show up at customs with this receipt and they wave you through. Very quick. I was at my connecting gate while the rest of the passengers were still waiting for their luggage. You can also use the NEXUS pass to speed through the TSA lines at the
airport. The NEXUS pass is not for the boat in general, you’ll need one for everyone on board.