I lived in Minot for a while when I returned from living overseas. It's a horrible place in my opinion but the people are nice.
Since you are just passing through I'd just stay at the Wal Mart for one night and go on to Canada the next day.
Swensons RV Sales has an RV park that is right on the road and is easily seen. But whether they do nightly rentals I don't know. They seem to cater mostly to the Oil Workers. And the rates in Minot are High.
On the west side of town on Hwy 2/52 is a Flying J which has lots of room for RV's without impinging on Truck Parking. I think they also have a dump. (but not sure)