calgary early breakfast downtown
Depends on what you're looking for, willing to spend, and where you want to go. If you're right in the downtown core and don't care to venture that far (because you are in town for business and won't have time, Red's, Blue Star, Diner Deluxe won't work for you. Certainly wouldn't work for me if I was looking for breakfast before a workday.
I'm going to throw out a recommendation for the Chowderhouse for breakfast. It's well-priced, good food, and opens at 7:00 am (google it for their menu). And if you're in town for business, it's in a nice location, just south of the corner of 6th Ave and 1st St SW (just south of Bow Valley Square) which is pretty central. Other options I can think of are Cora's right in Bow Valley Sq (on the fifth ave side), or if you're close to Eau Claire you can do 1886. Otherwise, if you're in town on business and are expense-accounting your breakfast anyways (of if somebody else is paying), head over to the main restaurant in the Westin and have their breakfast buffet. Haven't been in a couple years, but it WAS fantastic, so I hope it hasn't changed. I think it runs about $25 a person.
Finally, there are a handful of really good coffee shops in Calgary that also serve a nice breakfast sandwich or two. My personal choice would be to hit up Cafe Artigiano on either 6th Ave and 3rd St, or in Shell (3rd Ave and 3rd St). Both serve a fantastic cup of coffee, and their breakfast wrap will keep you going all morning.