It indeed still exists. It's located in the John Ware building, which is the same building that houses the Four Nines cafeteria and the Highwood restaurant. The selection does vary, and I recommend going earlier in the day if possible, as the shelves are quite empty by day's end. Not only can you get great baked goods and great prices, they have a selection of meats and deli products as well.
I went there on a open house last year.
The Marketplace was a highlight from the tour.
In the windows were the most amazing croquembroques Ive seen in Calgary
(much more impressive that that of cruffs!).
And they were very traditional as well.
The market place is very impressive since it is of course the students who make the products.