Well for starters considering Sigismund II is the last of the Jagellonion's, it's kind of premature to talk about the Thirty Years War considering a lot of what happens next depends on whether the Union of Lublin still goes through with an 'Anglican' style Polish church, who gets elected monarch (if an elected monarchy still gets established) and whether you just get an agreement that they'll go for a Catholic monarch and return to the church so long as religious freedom is guaranteed.
Well for starters considering Sigismund II is the last of the Jagellonion's, it's kind of premature to talk about the Thirty Years War considering a lot of what happens next depends on whether the Union of Lublin still goes through with an 'Anglican' style Polish church, who gets elected monarch (if an elected monarchy still gets established) and whether you just get an agreement that they'll go for a Catholic monarch and return to the church so long as religious freedom is guaranteed.
Or potentially Poland ends up having a civil war over Lutheranism v. Calvinism v. *Anglicanism v. Catholicism.
And of course the protestant powers mostly didn't get involved in the Bohemian revolt anyway. Though the possibility of the King of Poland being offered and accepting the Bohemian Crown may go up in this scenario.
I don't really know enough about this bit of Polish history to guess who'd be the likely candidates for ruler however.
First, sorry, I didn't know Poland and Lithuania hadn't formally united yet at the time. Still, as Lithuania was mostly Orthodox at the time, I think most of its population would support a Protestant Poland. Historically, Orthodoxs had far better relations with Protestants than with Catholics.
Second, the Church of Poland was planned to be Calvinist. It may have a Calvinist theology but a structure more similar to that of the Anglican Church. I don't think Lutheranism has any chance. It was despised in Poland because of it's association with the Germans.
Third, Poland would be in a much better position to intervene in the Bohemian Revolt than the Protestant German states.
Well, Calvin was invited by some of the nobles yes, but that doesn't necessarily mean that the resultant church is going to end up actually being Calvinist. You've got complications such as whether you'd see this be taken as an opportunity for an earlier instance of the Union of Brest- i.e. the Orthodox church structure that historically became the Greek Uniate Church could see this as the opportunity for a distinctly Polish unified church, or it might end up becoming strong supporters of the Pope.
Poland intervening in the Bohemian Revolt is probably going to strongly depend on how involved they are in Russia- even historically there was a brief attempt at what one might call Poland-Lithuania-Muscovy, and with somebody who isn't Sigismund II Vasa on the throne that might well be where attention is focused.
