American Conquest - Single Mission - The French Army
This one isn't so hard, even on Impossible Difficulty.
Your Cannons are the key to the initial phase of the attack. They can shoot at targets far beyond their vision range. You just have to find the buildings by clicking around the fog of war. Make sure you have you cannons in control groups to issue attack orders without having to move the camera back at them.
Once the outer Forts and Blockhouses are down, charge your Musketeers in, with your Fusiliers close behind them if the British try to push out. The British Fusiliers will be especially dangerous when allowed to concentrate, so charge your Dragoons in when they do to send them into disarray. Continue to destroy the inner defenses with your Cannons while you keep sending waves of Musketeers to mop up the British and storm the remaining buildings.