Wouldn't that trigger Article 5 of NATO? The Philippines versus NATO would be awkward for everyone involved seeing as they are a key US ally in the region...
Not necessarily. Article 5 stipulates an "armed attack" as the basis for a mutual response. Even if someone "declared war" on Canada without engaging in any physical attack then the other members of NATO may not be obliged to join us in the non-fight. And even if that other country attacked one of our naval vessels (or aircraft or forces), it doesn't necessarily trigger Article 5. Article 6 explains.
For the purpose of Article 5, an armed attack on one or more of the Parties is deemed to include an armed attack:
•on the territory of any of the Parties in Europe or North America, on the Algerian Departments of France 2, on the territory of Turkey or on the Islands under the jurisdiction of any of the Parties in the North Atlantic area north of the Tropic of Cancer;
•on the forces, vessels, or aircraft of any of the Parties, when in or over these territories or any other area in Europe in which occupation forces of any of the Parties were stationed on the date when the Treaty entered into force or the Mediterranean Sea or the North Atlantic area north of the Tropic of Cancer.
If our ship, or aircraft or forces were outside the territorial boundaries of Canada, or at sea in other than the North Atlantic or the Med then the same would apply, our allies don't have to respond. Example - Falklands.