I am an American cruising on Norwegian Joy Sept 7th. We have a friend who might not qualify for admission to Canada. If she stays on board the ship while docked in Canada (6 hrs) is that ok, or would she be prevented from taking the cruise?
You are entering Canada, even if not exiting the cruise to go on land, you still enter Canadian territory and require a visa/authority to enter.
From Alaska Cruises:
The Canadian government requires foreign citizens from most countries other than the U.S. to obtain a visa for entry into Canada. This law affects all cruises that make a port of call in Canada including most cruises to and from Alaska and the Pacific Coast.
This will be checked and you wouldn’t want to risk it.