The key issue/interest being that as global warming advances north, that area will become viable for new shipping lanes and mineral extraction.
Not mentioned, but probably on the minds of people thinking well into the next century, as global warming transforms the planet Canada’s Arctic archipelago (some 36,563 islands, of which 94 are classified as major islands) may someday be prime real estate for settlements like New Toronto and Very North Dakota and so forth and they’re gonna want better control of those waters.
Though if we ever reach that stage, the rest of the planet will be virtually uninhabitable and we’ll have likely started to abandon it for Mars or Krypton or something, so good luck Canada!
This enlargening likely won’t happen smoothly, if Russia and Denmark (representing Greenland) have anything to say about it. As with any coastline, all three nations are entitled to a 200-nautical-mile economic zone into the Arctic and the other two aren’t likely to just let Canada grab the rest of it all for themselves. Extending this default economic zone must be applied for and approved under the United Nations Convention on the Law of the Sea.