The Vancouver itinerary leaves Canada and then returns, i.e. it enters Canada. The Quebec itinerary leaves Canada and does not return, i.e. it does not enter Canada.
ArriveCAN is required to enter Canada. One needs to make a submission sometime in the 72 hours prior to boarding your flight, train, car, or cruise.
From https://travel.gc.ca/travel-covid/travel-restrictions/cruise
Cruises that are staying in Canadian waters or not returning to Canada
All travellers are required to take a pre-embarkation COVID-19 test before embarking on a cruise in Canada, even if the cruise ship is not leaving Canadian waters
Travellers who are staying within Canada throughout their entire journey or who are leaving Canada and not returning donโt have to complete ArriveCAN.
One must provide a port of entry into Canada.