If you're not used to the prairies, I've heard of some people getting agoraphobia from driving just outside Winnipeg because it's just so very flat.
Good places to visit are the Whiteshell or Grand Beach. An area that's still quite a drive but would be neat is Little Limestone Lake
Depending on when you'd be visiting there should be festivals just about every weekend in the summer. Things like the Sunflower festival, Corn & Apple festival or the Pumpkin festival are a fun time.
If you want something off the beaten path, Zip Lining in the Pembina Valley is a pretty good time.