With regard to apples there is a decent selection for most locales. The coldest spots, however will find it necessary to seek out the toughest of the lot. Among them are Dolgo crab, Ranetka crab and Siberian crab.
Siberian, malus baccata, is likely the most cold hardy. It has had some criticism in Alaska as being a bit slow in growth (too much so for some folks) but may be oart if the reason for its high survival rate. There are reported issues with compatibility in some variety combinations. There is anecdotal evidence that cultivars with crab in their ancestry are less likely have rejection. ..
..more to come..