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Niagara Falls is more like Canada's Vegas.

Anyways, as awesome as Edmonton/St. Albert can be, like others said, if you found Winnipeg difficult to contend with in the winter, then this city may not be best for you. The summers are excellent here as the city really comes alive and it is usually not too hot but still warm enough to enjoy summer activities (think 18°C - 28°C). St. Albert has its charms as a bedroom community if you like being close but not right in the action. It has a nice, albeit small, downtown with what I'm pretty sure is the largest summer farmers market in Metro Edmonton.

Calgary might be a good middle ground for you if you'd really like to give Alberta a try. It's a growing, dynamic city like Edmonton is, and while it does get cold there in the winter, there are regular breaks from it in the form of chinook winds that come from the Pacific Ocean. This can have the effect of a difference between -15 and +15 in the span of 24 hours and is a great break from winter. Summers, like in Edmonton, are mild but not usually hot and the city also becomes quite vibrant during the warmer months. Plus note is that the mountains are less than an hour away and the western suburbs of the city are basically in the foothills while the eastern suburbs are firmly in the prairie.

Of the BC options, I second (or third?) the Penticton idea if you want to try out the Okanagan region. Close to Kelowna's amenities but in a much nicer city. Nelson and Vernon are also options if you don't mind towns (though it seems you prefer cities). Nanaimo and Victoria are both good options too, though Nanaimo is a bit cheaper if I recall correctly and you have Vancouver on your doorstep (or a short ferry ride away).