In the given scenario, a cruise sailing from San Diego to Vancouver, a test taken prior to departure in SD would not meet Canada's current test requirement of no longer than 72 hours prior to entry into Canada, as the cruise length is too long for that.
DCL would have to have a way to test everyone on board within the 72 hour timeframe prior to arrive at Vancouver.
This assumes that the testing-to-enter-Canada requirement is still in place by the time the cruise comes along. Also, it is entirely possible that the Government of Canada will develop a protocol that applies specifically to cruises that are arriving, departing, or porting in Canadian ports by the time the 2022 season starts. Although cruises have been allowed to resume in Canadian waters since 1 November, there actually aren't any scheduled until into 2022 - the only ships now are ones that are small and below the passenger threshold to be caught in the rules.
For the poster on the cruise, Air Canada has a nice little website where you can plug in your travel cities and vaccination status and it tells you the travel requirements [i just used the default dates as a test]:
https://www.aircanada.com/ca/en/aco...updates/2020/covid-19.html#/entryRequirements
The current rule is "Effective October 30, air passengers departing from Canadian airports, travellers on VIA Rail and Rocky Mountaineer trains, and travellers on non-essential passenger vessels on voyages of 24 hours or more, such as cruise ships, will need to be vaccinated. These requirements apply to all travellers 12 years of age and older." (there is a brief transition period in effect but it will be over 30 November).
Therefore, under the current rule, no need for tests to fly from Vancouver to Toronto.
SW