South facing sites are difficult. Cold air, already not containing much moisture, is warmed and it's relative humidity drops even further. So evergreen needles/scales and tree buds dry out. The roots are frozen so can't make up the deficit. Reflection off of snow in late winter makes the situation worse.
It's not just the degree of cold, but the length of the winter, and the number of hours of sun. In Alberta we have about 2000 hours of sun per year, but have below freezing temperatures for about 6 months. (Our annual average is something like 6 C. No permafrost, but by February, you wonder...)
What trees/shrubs are candidates to use close to the south facing house in a zone 3 climate with about 6 months of below freezing temperatures. Candidates should have height to width of 2:1, and have heights that reach 7 to 15 feet.
So far I have found some success with Rocky Mountain Juniper, and common lilac.
In the answer please specifically address south exposure. I know of many shrubs hardy in zone 2 and 3, but few that will tolerate the above freezing air/frozen roots, 25 C variation between day and night temps of a living next to a south facing wall.
The following do NOT work:
Any of the cultivars of eastern white cedar. (T. occidentalis) such as Techna, Brandon and Skybound.
Any of the very compact spruce. Fat Albert, Nana. Small spruce even in the open tend to sunburn anyway on the south and southwest sides in late winter from direct and reflected sunlight. Compact spruce have more still air near the needles, and dry out more.
Mugo and Mountain pine seem to tolerate the winter warmth, but mugo is hardly upright, and Mountain typically gets 25-35 feet tall with time. Both species (Taxonomic lumpers consider P. uncinata to be a subspecies of P. mugo.) are highly variable from seed, with larger mugo grabbing at the eavestroughing.
Ninebarks generally have a bad rep in cyclic temperatures. They do well in the open in the Edmonton area, but have a lot of dieback in Calgary with it's frequent chinooks, and winter thaws.