The software from ALK Technologies (Co-Pilot and PC Miler) has the most extensive data built into it concerning trucking routes, low bridges, etc. However, you mentioned "rural" areas of Canada and I must advise you that the address database does a better job on these products for the more urban and industrial areas than it does in the rural areas. And that goes for the US or Canada. I'm not saying that the ALK software is not a good solution for big trucks, because it does a good job in many cases. However, Garmin or MS Streets have better rural databases, but do not take into account for big-truck considerations. Hope that helps.
Yes, I answered an old post, but no one ever did and I was searching for areas where my experience with the trucking-style mobile devices could possibly help.