Actually i have been quite impressed by the AI reactions.
What i did was, i took my entire force to take the left flank, negating their tactical advantage on the right side.
What happened was their entire infantry force withdrew all the way to the back of 'their ground', near some small village, and they lined up.
When i moved my units forward, i had a classic line battle to the left of the village. The units fired at eachother over and over for a little while, and then i ordered my units to move in with melee, as i charged my Hussars into their left flank.
Some of my light infantry i sent around to the right of the village to end up behind the enemy lines, but they got assaulted and routed by the enemy general before they could kill him, but my main battle line was slowly gaining the upper hand in the main battle.
Some of the American forces then withdrew from the battle, taking refuge inside a nearby building, which had to be fought about, and which was quite a long battle. Unfortunately i didnt have my cannons nearby, so far i havent found a single good position for them yet: no matter where i move them, they get almost instant-hit by the enemy artillery.
Anyways, as i fought about the building, the enemy general withdrew back to their original defensive position, where the artillery was still going strong.
I sent my dragoons after him, before i reached him i had them unmount, and move further on foot. The General apparently didnt notice my forces at the bottom of his hill, because my dragoons moved in, formed a line, and in 1 burst shot the general and his entire bodyguard (or what was left of it anyways).
Meanwhile i had my remaining infantry units perform a quick charge on the remaining artillery batteries. They had the time for 1 accurate shot per cannon, cost me some units but thankfully not to much. The ensuing melee saw the Americans massacred, and the battle was won.
The game rated it as a close victory, as this was still my first turn, and i was figuring out how to best use my units, which units to put where etc. Still, it was a victory, something i cant say about my naval battle skills which turned into complete and utter raep for me
The next round i tried a full frontal assault, just to see how utterly massacred i would get. I marched some soldiers to the left batteries, and they got into range close enough to take out 1 battery. Meanwhile i had my other main line units move across the river, one of them taking out the right-side batteries with riflefire.
I lined up my soldiers across the creek, and let them fire 2 rounds before moving them into melee. While melee ensued, i ordered my cavalry units across the river and take up position on the left flank, and take out the remaining battery. Then i sent them into the main battle.
It was a costly fight though, as all but 2 of my units were routed. The remaining units (grenadiers and some other unit) i ordered back across the river in a long line.
Previously the AI wouldnt move, but without artillery to fire at my forces, they came across the creek. Again a new line battle followed, untill an enemy unit went into melee and assaulted my units. They were routed, and my units charged after them. In the process, a second American unit got caught, and seeing their routing friends, that battle was over fairly quickly as well. Now i had routed their entire defensive position, but unfortunately i didnt have enough units to clear out the remaining units who were guarding the long flank on the left, and my soldiers were all shot down
I tried the grenadiers grenade-option once though, it didnt seem very effectful. But then i realised that it could only have been because i tossed them into the river, and the grenades didnt explode! So i guess the fuses got extinguished, because only 1 grenade went off. Now that's nice attention to detail!