my strategy is quite different.
First, get a Good general, those +3 when attacking are very nice... (once i have a +6... but it is rare)
then.. let the french to invade your territory... it means they would have serious supply problem... as the upkeep certainly is not enough. If they go deep into your territories, you should be happy as they lost more troops due to upkeep. Your country is large, and let them take a few province does not matter. You will take them back.
Then let your 'Good general' to attack them. Choose a good battlefield to attack, sth like plain and never mountain, send stacks of army WITHOUT general to support him. The reason is that, in case the battle is not going well, and you want to save/load (or cheating as sb say), your general will not be changed. If you reinforce with other generals, the general on battke would probably change if you load the save game again, may be a nasty one, which means it is not good.
It always result to a huge battle... sth like 200000 vs 300000.. the french would keep on sending reinforcement.... and in most case... due to your good general.. you would win....
Fight few of such battles, the french should be exhausted of their army. And always.. due to the larger size of french army, pick your battles wisely. Dont fight a battle that you know you will not win... or win with huge lost, you cannot afford that. And after a battle, I always send the brigades that are depleted of organization and strength behind the front line to have a rest until they are of gd condition. It is a bad thing to use exhausted army in another battle, esp when your army is smaller than the french one.
And dont forget to pursue their defeated army if it is safe to do so...so that they cannot reinforce in their homeland, destroyed armies are always better, isnt it?