they actually disengaged from Finland and gave them their first real national structure
tried to do the same with Poland but the Polish are un-redeemable Russian haters
Finland was an autonomous part of Russia as the Grand Duchy of Finland from 1809 to 1917. And yes, the national institutions such as Finnish as an official language (1853, prior to that one had to use Swedish in government), currency (1860) and the parliament (Diet of Finland 1809, but regularly convened only after 1863) have their origins in the Age of Autonomy. Czar Alexander I was rather smart in gifting the recently conquered Finns such an autonomy, since it was a better deal than the Finns had had under Sweden, hence making it less likely that the Finns would back up any attempt of reconquest by the Swedes. This goes a long way into explaining why Finland was happy to be part of Russia until the Russification at the end of 19th and early 20th centuries.
By contrast, the Poles had had their own Kingdom and Golden Years, only to be partitioned in the 18th century. Then revived as an (semi-)independent Duchy of Warsaw by Napoleon in 1807, only to be partitioned again in 1815. Hence, the Poles had a history of independence, a quite recent one at that. Furthermore, unlike in Finland where the autonomy was respected (or at least the Finns were left mostly alone), the terms of the Polish autonomy were disrespected almost from the get-go. This explains why the Poles were more eager to gain full independence again.
Nicholas I said: "Leave the Finns alone. It is my large empire's only province that has not caused me a minute of worry or dismay during my reign."
(Source: https://books.google.es/books?id=fVjC9CdKmXsC&pg=PA71&lpg=PA71&dq=Nicholas+I+leave+finns+alone&source=bl&ots=PyzPfdziIu&sig=N9qXfgerGHjRnq3FBjFK64BHqKc&hl=en&sa=X&ved=2ahUKEwjS276O2qPdAhVJWxoKHV_9CGEQ6AEwFHoECAgQAQ#v=onepage&q=Nicholas I leave finns alone&f=false )