Just thinking out loud, but the more I think about this, the more I think the bigger piece of the puzzle is actually political.
First, you need the kit, so build the heavy armed Ice Breakers with light weapons load-out as per Ex-Dragoon - QUICKLY.
Second, the Parliament needs to pass legislation declaring the Northwest Passage an environmentally-protected zone and set requirements for all ships passing through.
Specifically:
i) They must be escorted by one of our Ice Breakers as the lead ship - without exception or be subject to seizure and fine.
ii) They must have double hulls.
iii) They must carry proof of insurance that should they have an accident, they're covered for clean-up costs.
In short, buying our icebreakers is far less important that declaring the rules of conduct for all other nations
with the assets in place to enforce those rules of conduct.
Of note, I think that such a role sounds more like a Coast Guard Role than a Navy role, although I think adding a Harpoon-equiped Cyclone to the helicopter detachment (perhaps with 2 more transport versions of the same helicopter) would seem a good investment in deterrence.
I should add, that because I do consider the United States a key ally and someone we need to get on-board with this, that we offer a blanket exemption for nuclear submarine traffic so long as their Artic transits are part of North American Security Patrols and registered with the follow-on to NORAD, however only at the highest security clearance levels.
Thoughts?
Matthew.