There are good catamaran sailing conditions at Lake Newell, Alberta and you can join the Newell Sailing Club (located in Kinbrook Island Provincial Park) if you like. Club members own a variety of catamaran types including the most numerous SeaSpray, various Hobie models, various Nacra models and various other catamaran types. You can also sail out of the boat launch area on Kinbrook Island Provincial Park located on the east side of Lake Newell. There is a fairly good launching beach that can be a bit exposed with NW winds. Lake Newell can get winds that blow from all directions so expect a variety of conditions including wind direction changes, changes in wind intensity and different wave conditions. The park has a large campground that is busy in the summer. You can prebook your camping space and time on the provincial reservation system. The season is May to late October.
I'll give Newell (just outside of Brooks, so supplies are only about 15 minutes away if you're camping, need stuff for your car, etc.) some props here, and dsnell provided a pretty good summary.
There's one thing I'll add, though: It's a relatively shallow reservoir, and used for irrigation. That means there's agriculture nearby, and with the right summer temperature and wind conditions you're bathed in the prairie perfume of the liquid pig manure used to fertilize the fields. It can get pretty bad sometimes.