As you board the ship in Vancouver you will go thru US Immigration, a formality.. Will ask a few questions
A passport is the best way as you will encounter US immigration at Vancouver Aiport on way back
On the basis that I reckon you are British you most likely will have a passport! Canadian immigration is no hassle at all and,when we did Alaska with Princess, U.S. immigration took place in Canada Place cruise terminal and was a breeze. Stunning destination - enjoy!
Thanks for the help it is greatly appreciated. I was abit worried that I would first come across US immigration in our first port of call and if it turned out to be a drawn out affair we would miss out on any trips.