Empire of France
Kingdom of Svea
Tsardom of Russia
All of them has their own strong part. And their own weak part. Play them well. And you will find out the best strategy of all.
To add some flavour to the names maybe rename Great Britain to the United Kingdom (Or if the text allows, the United Kingdom of Great Britain and Ireland) or some veriety of it and Austria to the House of Austria or Hapsburg since the territories of that dynasty lacked any official name until the 19th Century when it became the Austrian Empire.
Also a question on the mods player factions, is there any chance on having more factions added to the game? I mainly had the United Provences, Spain, Poland-Lithuania, the Ottomans and Prussia in mind.
From the quick time I've read you sub-forum I see that your basing you factions on archetype play styles, Prussia of the time could add a new one: Prussian soldiers were trained to fire quickly and paid little regard to accuracy or even aiming, thus they fired quicker than other armies of the age but were limited more than other nations to short distance firing ranges due to their poor accuracy.
The Ottomans to could be heavily based on melee and cavalry combat.