Thomsons is the main breakfast/brunch buffet inside the Hyatt Calgary, and its one of the better ones I've tried. It is spacious, has a cool Western decor, and has a number of good items not common in hotel brunch buffets I've been to. Its on the pricey side at upwards of 30 CAD/pp though.
My faves:
Pesto skin-on-salmon: Pleasantly shocked that fish on a buffet line can be so soft, juicy, and well seasoned.
Roasted Veggies: Good variety here, including white asparagus.
Roast Beef: Never too early to have this! Well seasoned, tender, and so good with horseradish.
Corn Quinoa Risotto: Very good. Calgary is famous for their beef and corn. This dish is a healthier version of the Italian version and had a nice, pleasant sweetness from the corn.
I didn't like the yogurt parfait too much - yogurt was on the tart side despite the excellent toppings. Their dessert section was pretty impressive. In honor of Calgary Pride Celebration they had a nice rainbow Panna Cotta that was smooth and sweet.