[folivier]

The distance through Canada is around 2500 miles to Alaska if you cross in the west. The speed limit in most areas is 45mph and we drove that speed so we could slow down rapidly when hitting a frost heave. Most are marked but lots aren't. You'll quickly learn how to spot them in time to slow down. The biggest deterrent I think is the lack of large campsites. They are there but the caravans fill them up quickly. Best thing to do is download the itineraries from the caravan sites so you can avoid them.
Either way it is an awesome trip.
One tip if you like campfires and stay at Provincial campgrounds in Canada. Firewood is provided but it's not split so bring an axe. We had to scrounge around after people left to find split wood.