For me, talking of French plane, I think of 3 planes, mainly :
Farman F40, which soldiered from Verdun to Somme ("Nivelle Offensive")
Salmson 2A2 (present in most other flightsim : First Eagle and Il2 WWI) : for both the French and the US, and it is really pleasant to fly.
Caudron R11 (or R4 or Letord) : they would add a lot of gameplay as escort planes, both for the French who will have to maneuver the plane to "screen" the recon plane and for the German, as it may be a tough nut to crack
As heavy bomber, you can add the Caproni (night)
As to Voisins planes, though the 37 mm would be fun, remember it performed as a night bomber for most of the war
Of course, there are plenty of others (Dorand, Spad XI/ XVI ....), but they can be easily "replaced" by other types (Sopwith ...) and are less iconic, though if one of your main marketing target is depressive people with suicidary tendances, I am sure you can sell a lot of them :)