I *think* the Calgary Stampede might be going on then, that's definitely the highlight of any visit to Calgary. Also makes the city very busy, last time we went, we were driving to and from the west coast. We planned to hit Calgary for July 1 (Canada Day) and stay with my cousin - when we got there, my cousin was nowhere to be found! We wound up renting a hotel room, but we decided, since we'd be coming back in the middle of Stampede season that, while we'd like to see it, if we don't have a place to stay it'd be impossible to get one. If you are there for Stampede time, count your lucky stars that you have your brother's to stay at.
Other than that, I can't really think of anything either, other than all the people dressed up in cowboy hats and jeans in the city. Will make you feel like you're in Texas.
ETA: According to
their website it's on July 8-17 this year. So I doubt you'll be there for Stampede if it's in "a few weeks".