I am a Kuwaiti citizen holding a valid passport with a US tourist visa. I would like to go on a cruise around Alaska. The cruise stops at Vancouver, Canada for only six hours. Should I apply for a Canadian visa?
If you plan to leave the ship then you need a visa.
If you stay on the ship, you may not need one. But best to ask the cruise line, as they may require all passengers to have documentation to visit all ports of call even if you don't plan on going ashore.
Yes, you need to apply for a Canadian visa. The length of the stay does not matter.
Do I need a Canadian visa if I have a United States visa?
Yes, you will still need a Canadian visa (temporary resident visa) to enter Canada. A visa from the United States does not permit entry to Canada.
If you are a permanent resident of the United States and have your Alien Registration Card (Green Card) or can provide other evidence of permanent residency, then you do not need a visa to enter Canada as a visitor.