It would likely break away during the collapse of the Russian Empire by a nationalist rebellion, like Finland, Poland and the Baltic states.Imperial Russia could annex Manchuria on early 20th century and on 1922 or bit later it gains soviet republic status.
What Lalli said. Have Russia take Inner Manchuria in the 1850's at the same time as Outer Manchuria and before the Chuang Guandong filled the region with Han settlers.
Inner Manchuria is the Manchu heartland. Russia had to fight the entire Qing China for that, which is something they doesn't seem to be capable of in the 1850s.
It would likely break away during the collapse of the Russian Empire by a nationalist rebellion, like Finland, Poland and the Baltic states.
Inner Manchuria is the Manchu heartland. Russia had to fight the entire Qing China for that, which is something they doesn't seem to be capable of in the 1850s.
One thing to be considered: Manchuria was home to 36 million in 1937 IOTL, even more than the Ukrainian SSR. If the USSR were to annex it, they would be ~18% of the entire population. By 1945, there were 45 million "Sinitic" i.e. Han and Altaic people living in Manchuria, which would be ~21% if the USSR integrated it. I don't see it becoming an SSR with such large number of non-Rus, seeing cases like Poland.