The North West Passage clearly belongs to Canada. Its NOT a international seaway. For it to be an international seaway under international law, it must have been used frequently throughout history. It wasn't used frequently, its barely used even today, and its only starting to get attention because the ice is melting allowing for all year use.

Also, according to the UN law of the sea, the waters within 12 miles of the coastline are the waters of that state. The islands in the North, which are Canadian and not disputed, belong to Canada and therefore the waters around them do as well. It is an archipelago, so the islands are so close together in some areas that it is impossible to cross the North West Passage without violating the 12 mile rule and being in Canadian waters.

Therefore, it is internal waters and Canada can deny passage from any other country of the world.

Also, throughout history, the US sought permission most times its ships traveled through the North West Passage, usually accompanied by a Canadian ice-breaker as well. So, why seek permission from Canada if its an international waterway? Because you recognize it belongs to us, you just make the claim its international waterway when it becomes of "strategic importance," but still don't have any legal argument to back it up, because none exists.

The US hasn't even ratified the UN law of the sea convention. So if Canada boards US ships for violating internal waters, theres nothing you can do about it, because you can't complain to the tribunal which governs international waters until you ratify the treaty. But Canada can bring any other violators of its waters to the tribunal, and that ruling, which would probably side with Canada, would be binding.

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"Conservatives are not necessarily stupid, but most stupid people are conservatives." — John Stuart Mill