The North West Passage has never been an International waterway for the simple reason that until recently if was impassable to shipping.
There no history at all extablishing free international passage of shipping. It's an inland staight and all the fish and mineral rights belong to Canada and the Inuit.
You might want to check out a book on the law of the sea.
By the way, I've personally been at the helm of an American Submarine at the North Pole. Therefore, I claim it on behalf of the United States.