I do not believe that there were any REAL cavalry units, there were certainly no REGULAR British or French Cavalry. The best they had would have been mounted militiamen as scouts, the only real exception were a 200 man Quebec unit that was absent and played no part in the battle. The heavily wooded areas and lack of grazing precluded cavalry. I travelled through Vermont and New Hampshire in the summer and there was little to see but trees........
Still, they are a nice addition to a FIW game and give it the feel of a European war with all the fun of other troops.