Hyway 20 also known as the Trans Canada Highway is a good 4 lanes road.
Fuel is quite expensive in Canada, specially in Québec, Currently regular gas prices range around $5.00 to $5.10 per US gallon. In Canada fuel is sold in litres, current prices are in canadian dollars around $1.40 per liter, 1 US gallon = 3.785 liters and currently the Canadian dollar equals approx $0,97 US.
I recommend that you fuel you motorhome before crossing the US/Canada border
Have a nice trip,