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Hiya there is a website giving all info on entering Canada, click on this link http://www.justlanded.com/english/canada/tools/just_landed_guide/visas_permits/tourist_transit_visas and go to the section Who does not need a Tourist Visa? It states that citizens from the UK do not need a transit visa.
I've been to Canada many times but never needed a visa, but things may have changed since then. Really, you're best best is to check directly with Princess Cruises to make sure - you don't want to be caught short when you get there.