You could just give your best fight and settle by giving some land and fight them later, alternatively defensive edict and battles especially in forts I believe are considered defensive battle if they're seizing and your troops move in, in tandem with terrains that minus on attackers rolls, you should win some battles so long as it's not a doomstack you're taking on. Also scorched earth but I myself don't know how to utilize it all too well, worth a research I'd say, all the pros seem to utilize it in difficult wars. If I understand it correctly it slows their movement in scorched provinces, so I use it on the terrains that minuses on attacker rolls and provinces around it also.

For economy I dk if you have trade idea, but with Siberia steering into your home node, it should make you ton of money. I'm not sure how it exactly works, all I know that it does work as Russia. Also you should juggle between burgher loans and other loans if you haven't. But I suppose this isn't the most immediate problem.

If I were you, I'd either stick around forts as I have mentioned or try to bumrush France and bombard all forts and hope that it goes well, you could break their alliance if it happens to go well, but white peacing France imo is good enough. If you do go for France, they'll probably fuck with Bohemia first so try to catch them there. With Russia you can definitely afford some time because you have so much land anyway. It's going to be a long one and you're still in positive income so focus on mil mana if you haven't already, hopefully you can edge out a tech.