They and the Catholic Church, which would be overlapping entities.
Now, in OTL part of the Polish nobility (I’m talking strictly about the Russian in pre- and post-Napoleonic times) went to various degrees along with the new masters and part left, creating a sizable pool of the lands/serfs to be granted. Out of those who remained some became full-scale loyalists but quite a few did not. In the Kingdom, while AI was appreciated and the Polish ladies were quite popular among his retinue thanks for their more “French” style of behavior comparing to their Russian counterparts, the resentment did not go away. The Polish nobility tended to look at the Russians down their noses considering themselves more “European” (with or without a valid reason) and the Russians were not happy with the Alexander’s pronounced Polish sympathies: at least by the reputation, in 1812 the Polish troops were considered the most cruel among the invading troops. Plus, besides the fact that the Kingdom pretty much preserved its Napoleonic army, its government was insisting upon transferring to the Kingdom the Belorussian and Ukrainian lands “lost” during the partitions. So the whole schema did not make too much sense for either side.
Now, on a limited scale, up to OTL 2nd Partition or TTL Partition, a sum total of the ethnic Poles on the annexed territories is not too big and, while the Catholic Church is still around, they are lacking the “infrastructure” needed for anything serious: the areas are under the Russian administration, there are no Polish troops (the nobles who want to serve are joining the Russian army) and the peasants are generally hostile to the landowners. Situation in the urban areas is more complicated but even in the worst case scenario they are hardly a decisive factor, especially if the new administration makes some meaningful moves like eliminating nobility/church jurisdiction over some urban districts, etc.
Unless your main goal is to achieve a geometrical perfection making a perfectly round or rectangular state. 😜
First of all, there are no memories of two extra Russian-Polish wars and 1812 and, as I said, the Polish nobility in the region(s) is lacking infrastructure allowing to become a major problem instead of being a minor nuisance. Those who want to move somewhere socially have to adopt to the general system rather than trying to do the same in the separate national one. Quite a few Poles did this in OTL, some with a noticeable success, and I’m not talking about the top aristocratic types like Adam Czartoryski.
