Canada

Like the USA under the current administration / trends? Do allies attempt to annex allies via economic warfare and separatist influence campaigns? And if the states can 'flip' from ally to adversary, why not others?

The current global situation means that self-reliance for critical sectors is of paramount importance -- trade and globalism is fine for non-critical things, and for general collaboration on broader initiatives such as global warming/climate change (for countries that agree on it). Ferries, as civilian infrastructure, are not individually critical - if they fail for some reason, it's "bad", but it isn't military failure levels of bad. Today we may think of Germany as an ally, for example, but the AFD and far right have significant support there, and it's entirely plausible that within the span of the sub contract Germany will trend more like the USA is today. It's also plausible, although still relatively unlikely, that China could expand its borders and push for SK to be absorbed by NK as part of a regional conflict wherein the USA doesn't bother to support its traditional allies / values.

Additionally, I have far more confidence in Canada's ability to take on civilian ferries, and their maintenance in the face of global uncertainties, than I do in Canada's ability to maintain foreign made military vessels with far more complex systems. Ergo such specialties should be built up and maintained in country, by purchasing assets from internal companies.