Generally speaking, states try to avoid having critical dependencies on other states, because they become points of leverage for adversarial foreign policy. For the purposes of keeping America running, yes, we really do need to own icebreakers in the same way that we need to own powerplants, steel mills, chip foundries and and refineries.
In this case though we're talking about Canada - the Canadian and US economies are incredibly linked. Personally, I'm a Canadian who makes money examining the US healthcare market and reselling that data to other Americans - there's lot of crossover here.
Versus being quite literally held hostage by a non-cooperating foreign power for political gain?
Things like energy independence sound cute and quaint until you find yourself being taken advantage of at best, or ground to a halt during armed conflict at worst.
Yeah, and then we'll enter a cycle of repatriation when it gets painful enough. Generally speaking, it's precisely the bean-counter mentality of aggressive cost reduction (with a narrow definition of "cost") that gets us into this position to begin with.
