1831: Poland wins!

Unless, as I suggested, you get rid of those territories in 1815, in exchange for ???

That's the million dollar question. In case of Prussia, that would only be Posen (Poznan) and in case of Austria, it's Galicia-Lodomeria.
Both seem quite hard to pull off, unless Austria & Prussia have the intention to really punish Bavaria, Saxony, Württemberg etc. for being French puppets for most of the Napoleonic wars.

OTOH giving Posen and Galicia-Lodomeria would also be a too great of a (relative) reward for Russia, since neither Prussia nor Austria have suitable compensation options, especially when one wants to maintain a balance of power in Europe.
 
Give Austria back the Austrian Netherlands and Italy (except the Papal state), and give Prussia a connection to the Rhineland and Alsace-Lorraine. That would be a good compensation for loosing Poland.

Austria wasn't really enthusiastic about taking the Southern Netherlands back, they'd rather have more territories in Germany or Italy.

Again why would Prussia and Austria want to make their neighbour Russia too powerful?
 
Maybe the larger Poland (Napoleonic-era Duchy of Warsaw + Galicia-Lodomeria) might be more acceptable to the great powers if its ties to Russia are looser, perhaps it is established as a Russian protectorate.
 
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