I would be less concerned with the temperature and more concerned about snowfall, and the potential for melting snow and ice.

Being comfortable and knowing how to drive in snow and icy conditions is important - allowing more room for stopping, driving slower (despite what others may be doing), etc). Having winter tires is important (but not required), but I do not know if rental car companies switch tires, I suspect not. All season tires will require greater stopping distances (winter tires too, but all seasons more so)

In the Cities snow is removed on a regular basis, but if you are here during a dump of snow (as is happening now), expect to take longer to get somewhere.

The highways are usually pretty good and very well maintained. You do have too watch out for black ice, particular in certain areas where the highway is exposed to wind (areas between Red Deer and Calgary in particular). It is important to drive for conditions and your comfort level.

As for walking, both cities will be fine, but you should dress for cooler temperatures - toque, scarf, mitts, warm jacket etc. Even though sidewalks will be cleared they can be icy - leather soled shoes are not recommended.

More so in Calgary, you can see temperatures warm up which brings melting snow and ice as it cools.

The weather here can change quickly in both cities.

Despite all that, there are over 3 million people here that live with the temperatures on a daily basis, and it is not bad, sure it would be nice if we had beach weather all year but we don't. We just dress appropriately.