We have been to Riding Mountain National Park several times. The main full service campground Wasagaming is at Clear Lake. This summer (2017) with free passes for entrance to all National Parks for everyone I expect it will quite busy in July and August. Having said that if you are unsuccessful in getting reservations prior to arriving there is a private campground just south of the park entrance in Onanole, approx 10 minutes from Wasagaming. There are also no service (basic) campgrounds in the park, Lake Audy being one where one might see Bison roaming wild. Further north of the park in the town of Dauphin approx 40 minutes there is also a full service campground.
Another Manitoba site that deserves mention is Winnipeg Beach Provincial Park at Winnipeg Beach. It has a large full service campground with 50 amp service, here you will see the 10th largest freshwater lake in the world. On a clear day you might be able to see the other shore across the lake. Safe travels. :)