I haven't stayed in this particular Marriott, but I understand it generally gets good reviews. It is well located,, at the edge of the downtown's eastern end, right across from the Calgary tower. It is a short walk to the light rail transit system, near some restaurants. If you like Thai, go to Thai Sa-On (a couple of blocks south and west of the hotel). What kinds of things do you like to see? The summer parks don't generally open until the May long weekend, but lots to do before that time.
I just came back from Calgary. This hotel is right on the parade route for the annual Stampede they hold in July. The hotel is great. The employees are very helpful. You can walk to lots of restaurants, cafes, park, museum and theater from there. Nearby spots have rooftop dining or sidewalk dining for good weather. There is an indoor shopping mall nearby also. If the weather doesn't cooperate, the hotel has good food. We drove from Calgary to Galcier Nat'l Park in Monana. It was a great trip.