From Calais, head east through the WWII beach landings (I dont have expereince there), then turn south and pass through WWI battlefields (Battle of the Somme, Lens, Arras, Baupaume, etc). Look up "Beaumont-Ham Newfoundland Memorial" or "Canadian National Vimy Memorial" for an idea of WWI memorials. Lots of info on the Internet regarding WWI monuments, memorials, cemeteries, that I can't possibly do them justice. Are you British? This was an area where Britain was very involved during WWI (and thus have many memorials).
Good map for this area is Michelin Regional Map 511 Nord-Pas-de-Calais, Picardy. Scale is 1;200,000 (as all their Regional Maps) and shows all roads outside of towns. We use google maps on our cell phone to navigate into/out of larger towns and occasionally "ask for suggestions" between towns, though generally we ignore the suggestions - but it can be helpful as it will show route profile.
I find riding time on Google maps to be accurate to somewhat conservative, but yes, it does not include time off the bike. And from my experience touring some of the WWI area we definitely spent time off the bike.