Yeah, that's a difficult level, but it is doable on Impossible. Basically there are two strategies that can work pretty well:
1. Artillery man. Spawn at the closest point to the French, and grab the artillery. Immediately kill any armored unit that comes into sight, if none are in sight go for infantry. At the very start, aim for the area behind the bridge and try to get a few guys that way. You can hold them off for a pretty long time this way if you hit the armor quickly enough, enough that the ticket count goes in Germany's favor.
2. Sniper. IIRC this isn't quite as effective, but at least you can respawn (unlike the artillery that after it is dead is, well, dead). Take a position either by the artillery or close behind it, making sure you have shelter for reloading and hiding from Priests, as well as extra ammo for resupply, and target anyone who comes into view. The bridge is a good default target. If you shoot well enough, the rest of your team ought to be able to hold off the French armor.
Rambo-style charges aren't really effective on this map. You spend too much time waiting to respawn and too many times the French snipers will kill you before you kill anyone, and Germany gets overrun pretty quickly. The key is not dying. Eventually the French will reach your point, but if the tickets are in your favor by then you have done well.
I know I've won this one before on Impossible AI, Normal Troop Ratio, and Normal Death Penalty. Been awhile since I played Monte Cassino, but I think my memory of the map is pretty accurate.