According to the ideology, the USSR liberated the countries.
For example in Finland (which was very poor at the time) there were quite a few communists who were keen to be "liberated" by the USSR, and thought they'd get a better and more fair lifestyle in the USSR. But they were not the majority.

I think the situation was the same in the Baltics. I have some distant relatives of Estonian origin. They were farmers. Everyone in the family moved to Sweden in 1945 because they had a bad view of the USSR. However one brother was happy to stay there. According to my grandfather, he was a communist. Lots of people in the Baltic states too, were communists. The Baltic SSR states were not run by Russians, but by local people who were communists.

Secondly, Stalin was just as much a national leader/dictator who wanted more power, influence territory... as he was a communist.

Basically a lot of the things that the USSR did in the the 30s - 50s have a lot more to do with what Stalin wanted, than what was necessarily communist idelogy. For example, communism does not say that people should be sent to labour camps in distant locations. That was just Stalin continuing an old Russian tradition from hundreds of years back... but greatly increasing the scope because he was not willing to accept any dissent.

I don't know any details of this, like I said - in school I was told the version that they were liberated from nazism by the Red Army and then incorporated into the USSR - end of story. I was aware that some people disagreed with this view though and in the 1990s the views of the Baltic people became clear. But the Baltics practically never were independent countries, always part of other countries. Just for about 20 years or so, they were independent. Russia, Sweden, Germany, Poland and probably some other country have been running part of that area for many decades.