I absolutely agree that pasture based livestock farming is going to be the best way to provide protein AND vital fat calories if the weather turns funky. Some shelter is vital, mostly to provide protection from dampness (animals with wet haircoats lose body heat much faster than if they remain dry), but even heavy brush and dense trees can be sufficient.
My son is currently outwintering a pair of pigs; a huge sow which is a cross of more modern breeds, and a little boar who is some odd, primitive type (I can't remember the exact breed right now... he has a curled up, pushed in snout, and thrives on grazing... he doesn't root nearly as much as most hogs). DS lives in northern N.Y., where they can get up to 10 feet of snow, although their proximity to one of the Great Lakes means their average lows rarely drop below -10.
He built a small, uninsulated lean-to shelter for them, and they are thriving. He butchered 8 young hogs last fall... managed on rotational grazing plus about 5# of grain each (made into a fermented slop daily) plus garden waste all summer and pumpkins from early autumn until slaughter. They averaged 300# dressed weight, and he got close to 300# of lard off the group.
While these days people have been obsessed with "low fat" diets, fat is vital for health and survival, and animal sources are much more capable of providing significant amounts, without humans needing to burn large amounts of calories in the production process, than most vegetable sources. Nuts, as Faroe mentions above, are an exception to the rule, but can be susceptible to insect damage and much predation from birds and squiirels. But lard and butterfat from a dairy cow or two is nearly priceless.
I've mentioned before how we had an Irish Dexter cow (one of those old, specialized European breeds mentioned above) go feral on us. She roamed our farm alone all winter, utterly unbothered by the packs of very large coyotes (they can reach 90#) common here, or by the 4 feet of snow we had most of the winter. She pawed through the snow and grazed on 3rd crop hay which we hadnt harvested, and when we were finally able to catch her that spring, she was fat as butter.
However, we already live in a very short season area... we commonly only see from 90 to 110 frost free days, although we will occasionally see a couple days in the summer reach the high 90s. And we can grow most common garden crops, including tomatoes and peppers, although we can't easily grow lima beans eggplant, peanuts or sweet potatoes, and melons can be tricky. But I've grown large crops of open pollinated grain corn and popcorn, consistently. And we can grow winter wheat and rye, as well as oats.
Potatoes are an excellent, reliable crop that produces a LOT of nutritious bulk, IF we can kerp blight from killing them.
We also have large numbers of sugar maple trees to tap in spring, and honeybees seem to do well, although because of our much shorter season, we obviously have to leave a lot more honey for their own use. Even so, we got over 11 gallons of honey from 2 hives this year for ourselves, despite one of them swarming once, and then requeening itself in August, which reduced the total honey production.
The major issue about living in colder climates is the necessity for supplemental fuel for warmth (for people), Although modern super insulation materials and techniques can hugely reduce the amounts needed. The same woodlot that produces nuts and maple sugar provides hardwood for building materials and firewood.
Add some sheep for wool for clothing (as well as fleece from butchered lambs for meat- tanned fleeced make incredible bedside rugs, as well as bed pads for staying warm on bitter nughts), and possibly rabbits for furs, and it's not nearly as impossible as peopke think, although most of your time is taken up in basic subsistence tasks. When our kids were small, I raised rabbits for meat, and tanned most of the hides from those we slaughtered. They had rabbit fur slippers, mittens and hats, which they loved. I had some Rex rabbits, whose fur is an incredible plush, "cut velvet" texture, and While they aren't as efficient for meat production as the breeds bred especially for that purpose, they're certainly adequate.
Geese also are incredible low input meat sources... goslings will dress out at 6-8# of meat (with a high fat content) grown on nothing but grass. And goosedown is an invaluable insulation for down comforters, mittens, and outerwear, although modern "downproof" fabrics make it even more practical.
For those who haven't read it, get a copy of Laura Ingalls Wilder's book "Farmer Boy" ... it describes her husband Almanzo's childhood in far northern N.Y. state, in a town called Malone. They got (and still do) many feet of snow, temperatures down to minus 40 degrees on a routine basis. And yet his father had thriving dairy cattle, sheep and horses. The book is really an excellent primer on surviving in a very short season, cold area.
Summerthyme