I would suggest using a period map in conjunction with a more modern military survey map, and/or Google Earth to generate the real terrain in a ten mile square area. I use a hexagonal overlay (1" hexes on a period map sized to scale 1" equals 10 English miles) You could just as easily scale it with French Leagues or Prussian Miles, as the period maps have all these keys on them. (See David Rumsey map collection)
Consulting the period maps, including Allison’s Atlas, in conjunction with modern satellite imaging can give you a very fair picture of the terrain in question as the armies come together.
Once opposing forces are in proximity (one hex, based on the principles of scouting espoused by Clausewitz, Ney, DeBrack, Jomni etc. http://www.napoleoniccampaigns.com/ The modern maps are consulted to generate the terrain.
Some study is required here to determine which commander fairly knows what, in a wargaming context.
By this, for example, I mean, French light cavalry officers and other dedicated officer scouts were well trained in sketching the terrain ahead and passing that information back to corps and army command efficiently- as well as directing deployments based on that information when posted at the head of the columns. These highly skilled officers were the reason for French advantage in speed of deployment in many meeting engagements whose names far outnumber the set-piece battles that are more famous. Certain types of English, Austrian, Russian and Prussian officers were adept at this too- depending on the theater and period. Giving the advantage to one side or the other in terms of terrain knowledge should be weighted accordingly.
For Example: In Bavaria in 1809, the Austrians possessed better maps, and more complete knowledge of the terrain the Danube Campaign was fought over than the French. However, their ability to use this information was compromised by their staff system. Therefore, it’s fair to say that both sides have an equal chance of knowing what is ahead of them in this campaign. The Peninsula would be different- for many reasons the Brits would be given a terrain scouting advantage- and so on.
Once the terrain is determined, the commanders issue deployment orders based on what they know (or don’t) Objectives are determined, and orders issued. At this point the clock starts ticking at the grand-tactical, rather than the operational level. Map movement is transferred to a magnetic dry-erase board marked with a scale 10 mile hexagon, and the magnetic counters of opposing units moved there over the above researched terrain. This can be done on paper, or cpu if you have the software and skill (I’m learning!)
The rectangular ‘battlefield’ inside that hex, scaled to the available table-top would then be decided upon by the player with the movement initiative in their favor, as determined by your rules system.
Then, I recommend using a system designed like Todd Fischer’s Republic to Empire for then transitioning units from march column to tactical formations.
Units that are not moving on to the table at any time are still tracked on the dry erase board. This facilitates ‘off-board’ movement’ and with an umpire this works very well- there is real fog of war, as either side is given information based on what they can see, and their scouting ability (experience & numbers).