My vote has to go with Calgary. Its a big city without feeling like a big city if you know what I mean. Jobs are in abundance right now in just about every sector. The one thing that I really loved is that nature is a short drive away. There are also tons of paved trails throughout the city (250 miles worth) to go running, biking, or rollerblading on whenever you feel like getting some excercise.
I should note that I have also lived in Toronto, Vancouver, St. Catherines, and a few other places not worth mentioning and would still choose Calgary over them any day. As a matter of fact I'm heading back to Calgary in a few months.
I should add that I have also heard god things about both Montreal and Ottawa but since I have never stayed in either place I cannot recommend either.
Best of luck....
Drifter