Well, I thought this had already been established?

The press release said of the 10 playable factions, there would be:

Britain
France
Spain
Prussia
America
Ottoman Empire
Russia (reference to Peter the Great)
Sweden (reference of Charles XII)

So 2 are missing. Chances are that one of those has got to be Austro Hungary. The other one could be The Netherlands (though in decline throughout the period), Portugal? Maybe Mughal India?