AHC/WI: Russia and Poland-Lithuania United Into A Single Country Peacefully

Instead of the wars and conquests against one another, could Russia and Poland-Lithuania instead unite though marriages between one another and whatnot? There’s definitely been a tense relationship between the two, but could they possibly overcome that and become a united nation peacefully? What would the structure of the government look like? And does this enable the nation to expand with greater ease?
 
Orthodox nobles were not allowed to be elected as Kings of Poland (if I recall correctly), and, similarly enough, Catholics could not be Tsars of Russia.
 
It could be a union where all three countries have autonomy.
I seriously doubt such a union would be long-lasting or could even be achieved peacefully.

Poland had plenty of troubles keeping Lithuania in line already, now consider adding a third partner to the mix who is both the wrong religion, more populous than the other two partners added both and also really wants to annex territory held by the first two (Belarus and Ukraine, that is).

It's like throwing two scorpions into one glass.
 
I seriously doubt such a union would be long-lasting or could even be achieved peacefully.

Poland had plenty of troubles keeping Lithuania in line already, now consider adding a third partner to the mix who is both the wrong religion, more populous than the other two partners added both and also really wants to annex territory held by the first two (Belarus and Ukraine, that is).

It's like throwing two scorpions into one glass.

Well then whatever then...
 
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