If that's what the US is basing it's legal claim on then it will fail on technicality. The illustrated route through the Northwest passage clearly shows it traversing waterways surrounded on each side by Canadian territory, not between two neighbouring countries as listed in the 'precedent' examples.
It would seem more a case of something like the Makassar strait in Indonesia, or the Cook Straight in New Zealand, where the passage is bounded on each side by territory belonging to one sovereign nation.
It's not just other country's waters but also the 'High Seas':
> The United States position is that the Northwest Passage qualifies as an international strait, thus giving foreign ships the right of transit passage. In order for a strait to meet the qualification of being international, there are geographical as well as functional criteria. The geographical criterion is that of a waterway between adjacent land masses that links two bodies of the High Seas or EEZs . Its functional definition, not laid down in UNCLOS III but based on customary international law, defines the criterion to be a strait used for international navigation .
See UNCLOS, Articles 37 and 38(1) & (2):
So while it is internal to CA land mass, the argument goes that innocent passage is allowed through because there are 'High Seas' on either side, and so allowed for functional usage. This is why Spain, Morocco, and the UK can't simply close off the Strait of Gibraltar: there are international waters on either side, and so freedom of navigation is mandated. This is also why Greece can't just close off the Aegean Sea, even though they own the archipelago: freedom between the Black Sea and the Med.
I believe that that the Beaufort Sea (US EEZ?) and Baffin Bay (DK EEZ?) will be used for the purposes of the argument.
The US wants to open up the NWP, because in theory that would also open some waters around Russia as well.
I have no idea how valid this argument is, but that are the technicalities of it. IIRC, the EU holds the same position.
(Disclaimer: I'm Canadian.)
The Cebu Strait is between various islands, all owned by PH and with no competing claims:
The Alor Strait connects waters controlled by ID