At least for the US why not keep one or more nuclear missile subs in the Great Lakes? Lake Superior alone covers 31,700 square miles to an average depth of 483 feet. It’s far to large an area to target with a first strike and well protected from non US/Canadian forces. Edit: A US/Canadian treaty demilitarized the Great Lakes. https://en.wikipedia.org/wiki/Rush–Bagot_Treaty
What could a dozen 1MT warheads, sunk to a depth of 100ft, do to submarines anywhere in the Great Lakes? Shockwaves travel through water much better than through air. Water explodes into steam in a way that air doesn't.
My intuition is that you actually could pretty reliably paste a sub inside the Great Lakes using some nukes launches from Russia. The lakes may just not be deep or big enough to hide in.
This is leaving aside the treaty, the lack of freshwater sub technology, the long time to retaliation due to long range, the lack of a sub facility on the lakes, and the unnecessary nature of the whole enterprise (if the US lost 1 boomer sub to an enemy they could bring the others into a defensive posture making them practically impossible to hunt down, to preserve 2nd strike capability).