On the your planned route(in ND, do not know about Canada) roads are good. No problem with fuel. Oil field traffic has dropped way down and that was mostly west of Minot. Minot is still rebuilding from their flooding so places there are quite full.
45 miles north of Bismarck, 70 miles south of Minot, is Washburn. There is a very nice Lewis and Clark Visitor Center. A mile or 2 past that is a reconstructed Fort where Lewis and Clark spent the winter, very interesting and all worth the stop.
Go to Bismarck like you plan, spend a couple of nights at Ft Lincoln State Park. Take in Custer's house, Mandan Indian Village and the state park. All very nice.
Go west to Medora, only about 140 miles from Bismarck, spend the night there taking in the pitchfork fondue and musical.
From there to Spearfish is only 200 miles. Longest stretch with no fuel is only about 110-115 miles, fill up in Bowman. Long straight drive on good road. If you are going to stay in the Black Hills a few days I would recommend going father south into the hills. Spearfish if on the northern edge and it is about 85-90 miles to Custer. Long days of driving to do much site seeing. Many nice campgrounds all over. Hill City is about the middle of the Black Hills. Endless things to do in that area.
Enjoy the trip.