North American Communities
There are 3 phases of note:
1. Initial Rash Survival - Can your community self quarantine fast enough and for long enough?
Lots of places in the New World meet this criteria, villages & towns in the Far north, islands, but will those who can understand and DO IT? Savagely enough, fast enough and with enough
healthy paranoia?
2. Short Term survival - Post Apocalypse. is your region in a favorable place where you can survive the after effects and survive for a coupe of years
While you do not necessarily need hundreds of miles of water, apparently a 4 season climate that gets snowy- cold is very helpful. Obviously having access to lots of pre-apocalypse resources will help too. It's unclear what the post rash troll/demon things need to stop them. Is a large river enough? Are hundreds of km's of grasslands sufficient. Can they cross ice?
What's the infection/survival rate of wild animals, it's not 100% we know by inference.
3. Long term - Got enough people to maintain enough technology to have a stable civilization?
Civilization, even a harsh "geared down" survival mode one needs LOTS of skills. Butchers, Bakers, Farmers, paper makers, blacks smiths, refiners&Smelters , miners, dentists, Doctors, loggers, ....just making a graphite pencil takes, like 75 industrial processes...
You need enough people and
enough of a birth rate to accept attrition losses that would seem INSANELY high by 21st century euro-american standards. Basically, women had better be having 5+ (surviving) kids EACH, and that means safe areas with decent food supplies. (Hey, there will not be any birth control, and the nights will be very long. Rural Quebec province back when it was very Catholic up to 60 years ago it was not terribly unusual to get married at 16-19 and have 6+ (or more, surviving) kids. I've met older people from families of 12+ kids it wasn't odd or unusual. Healthful climate, lots of food.)
So What do we have:
Mainland North America: Mostly a dead zone, most of it is too warm it would seem.
Islands both Water surrounded or a land surface that is easily controllable.
Victoria Island (West Coast) - Will not survive Phase 1. Too many people. Too close /easy to refugees from Seattle/Vancouver. Might be possible to cleanse later if there is any population pressure. Also too warm, probably.
Hawaiian Island chain: too many people, improbable they can quarantine. Some of the secondary islands might be a possible refuge for the remnants of the US Pacific Fleet that survive Phase 1. Iffy. Waay too warm.
East Coast:
The Rock. aka Newfoundland aka "the Other Iceland" possible, really no worse physically than Iceland, but doubtful that they could quarantine in time, the Canadian Navy out of Halifax MIGHT be able to go "off the reservation" and enforce something, it's a pity because otherwise it's a pretty good choice.
Prince Edward Island, not terribly cold, but only one
very long bridge to the mainland. Hard to maintain a quarantine but the big east coast army base Gagetown is "nearby" in New Brunswick and a rogue army unit might be able to bottle it up in time and energetically defend it. Long term, it's ideal, great farming, not really close to any serious population centers.
Anticosti Island in Gulf of St. Lawrence. No infrastructure, no one ever settled there in any numbers. There's a reason. Wretched weather, iffy farming.
Lac St Jean/Saguenay Fjord: Ideal except for one thing. It's got more electrical power than you can imagine, it has a small town, it's been farmed since the 16-1700's, the winters are
BRUTAL. It's surrounded by dozens of miles and miles of nothing
and not much else. Access is limited to a couple of roads. The Royal 22nd Regiment ( Mechanized Infantry) is located nearby at Valcartier Army Base. They could EASILY seal it off from the south. The problem: kind of close to Quebec City, but really, that's no worse than Stockholm/Mora. Sealing off the North Shore road also protects the communities down the gulf coast. And they could retreat up the Fjord for a better tactical position. Europeans take note, and look at the maps, huge distances, low population density.
Inland:
Depends how the great plains serve as a barrier and if a quarantine could be engaged and enforced fast enough. There are number of smaller towns out in places like Manitoba and Saskatchewan that A. Have harsh winters. -40C is _common_, highs of -20C for weeks and weeks. B. Are miles and miles (and miles) from "big" cities (that are not so big: Winnipeg, Regina, Saskatoon) and that C. Have lots of old (and new) order Mennonite farmers who know how to farm without that much "tech stuff". E.g Brandon. Summers are warm, hot and dry.
Also Inland: The Lake Superior & Lake of the woods littoral, places like Thunder Bay, the more isolated parts of the Michigan "Upper Peninsula", the bit to the north of Wisconsin... limited access, if someone slammed down a quarantine , hard winters, 100's of miles from large cities. People used to being ignored and snowed in. Again for Europeans, look at the maps, the size of the lakes & distances is astonishing.
Most of these places would not make it, frankly , the Phase 1 hurdle is VERY High, the rash is incredibly contagious and does not appear symptomatically until its far too late to matter. It's unlikely any authority (military or civil) in North America will react fast enough (proactively enough, with enough paranoia, and enough disciplined savagery) to quarantine successfully. But that is true for EVERYWHERE. It's hard to tell non symptomatic people, "go away and die, or we will shoot you right there. it's even harder to do" Would you enjoy shooting and killing healthy looking women and children? That's what it will take. No exceptions. No Mercy. Mass murder for the greater good.
On the other hand, some Swedes, Danes and Finn's survived, so it is theoretically possible.