Stampede and the Stampede grounds are probably worth a day especially if you get tickets to the Rodeo and Wagons.
Sports wise that is the start of the CFL season at McMannon stadium; I like the CFL but to some it is an acquired taste.
The Glenbow museum in downtown Calgary is worth a look. Fort Calgary is also good. I’d rent a bike from Eau Claire market (not that good as a place in it’s self) and then do a ride up / down the Bow River. For some more adrenalin activity go to Calgary Olympic park and rent out a AM bike and play on the trails for a day.
I think (but I’m not sure) that you can hire canoes and go for a canoe on the Glenbow lake from heritage park. Failing that there are plenty of companies that do shuttle services along the Bow river for canoeing and floating. They drop you at the NE and pick you up in the SW. Enjoy a float and join the rest of Calgary in trying not to get busted for having alcohol in the boats…. A good activity to people watch. If it’s your thing then the fly fishing is world class within Calgary and a number of companies run trips locally.
If you can do it all I would hire a car one day and drive out to the mountains and back. A nice loop would be to go South through the prairies towards long view (on the Cowboy trail); come back via Highwood pass (Highest road in Canada). Gives you a mix of Alberta and rockies whilst avoiding the area around Banff. You could extend that trip by visiting the Head-Smashed-in Buffalo jump site neat Fort Macleod.
I’m not sure but I think some companies do day tours to the Dinosaur National park and Drumheller area. As a geologist I love those places and the Tyrell Museum is one of the best paleontology museums in the world (but if you live in London you’ll have been spoilt by the national history museum.)
Hope that helps.