If we look at the primary role of the navy as being to defend Canada and to protect the national rules-based order internationally, that's a pretty fair and simple summary. To believe that a navy is useful in both locations, it helps to understand not only that there may be a threat some day, but that there actually is potentially one today, that there are capabilities that could be turned against the international rules-based order today.
Happily, there's a country that is satisfying that, and another that's perhaps getting ready to. Look at Russia and the actions it's taken over the last six years. It has built up quite a list of activities contrary to the international rules-based order. Not only that, but as a member of the UN Security Council, the UN isn't going to be doing anything about it. It's what NATO does to deter the actions of Russia that matters.
Although we all talk about needing ships that are capable for war fighting, and we believe that quite honestly, perhaps most important is that the ability to wage war, matched with political intent from something like the alliance, means we don't ever wind up going there—the deterrence is effective. That's why there's a ship today reassuring the European allies, and a ship today then deterring.