climbs and such are one thing (and not insignificant) but considering you want to do trips with your kids, another super important factor is how travelled a given stretch of road is, and or what sort of shoulders are there? Is there a lumber mill nearby so you might be dealing with loads of lumber trucks, camions des pitounes, or dump trucks--this sort of thing. For me, this is the stuff that is harder to ascertain from looking at a map, but at least nowadays we can get pretty good info about routes already toured on by looking up stuff on sites like CGOAB.

As for difficulty as in steepness etc, all I know is that when I did Gaspe in 90 or 91, I got some really unpleasant surprises with some killer killer hills that were just murder getting up, and dealing with too high gearing, too much stuff. Looking at maps, I had no idea some sections were so bad. A few summers ago when I did Montreal to Boston, I didnt take the time to go over google maps or whatever for climbs along the route, but I think from more experience at looking at a map and figuring that a road would have a much higher chance of being steep due to the the layout of how the road went.

I dont know if its still the case, but Michelin maps in France 20 years ago had those neat little arrows or chevrons on climbs and descents to give an idea of how steep it would be. One chevron=a bit steep, 2=more, and 3=pretty darn steep. Really handy for giving a heads up. Today, realistically I see reading trip reports and such as the most reliable way to see how a route is, if not it comes down to doing the computer thing, or back to reading maps in a way to see how a road follows rivers and such, and or being lucky and seeing maps that show elevation and stuff, and or topo info to a degree.