The answer to your question ranges from “perhaps” to “no chance”, depending on how you define invade and what you would consider successful. If landing a small raiding force on a lightly defended part of Hokkaido to cause some momentary chaos amidst the local Japanese command satisfies your requirement, then yes, it is plausible. An actual full-scale invasion, however, would not be plausible, nor successful.
In June of 1945, realizing that the United States would eventually have to invade Japan, Stalin expressed interest in a Soviet invasion of the northern island of Hokkaido. When Stalin approached his top commanders on the issue, their responses were unanimous in that it would be of great risk and logistically impractical. Field Marshall Georgy Zhukov, stated that he would need four armies, consisting of six divisions each, which would have to be taken from the forces planned to invade Manchuria, greatly diminishing their strength.
Chief of the General Staff, Marshall Aleksander Vasilevsky stated that an invasion of Japan was “extremely dangerous and utterly impractical”, and that “the Soviet Army should not expose itself to the strong Japanese defenses on the main islands.” It was also noted that an invasion of Japan by the Soviets would be a severe violation of the agreements made at the Yalta Conference, a violation that would not be taken lightly by the United States or Great Britain.
The logistics of transporting soldiers and material to Japan was also a monumental task, one of which the Soviets were not capable of. The Soviets did not have a sufficient arsenal of landing craft for an amphibious invasion, nor did they have the naval or air capabilities to adequately establish superiority in the area. Landing craft were being provided to the Soviets by the United States as part of Project Hula, however, this project had only recently begun and would be compromised if the United States saw the Soviets going against their interests. Perhaps not of any lasting effect but a few of the landing craft provided by the United States were sunk in operations against the Japanese in the Kuril Islands.
Considering the American invasion of Honshu in March of 1946 would have been on a scale that dwarfed the Normandy landings, it becomes apparent rather quickly that while the Soviets may have had enough men to throw into the meat grinder, the logistical requirements were far too great for them to achieve any success.
This information and much more on the topic can be found in the book, Hell to Pay: Operation Downfall and the Invasion of Japan, 1945-47. By D.M. Giangreco. This is an excellent read that covers all the aspects involved with military operations regarding Japan in the final stages of the war.
You may be interested in these previous threads. One with a post from myself and another by /u/restricteddata
The short of it is that yes under pressure from Moscow there was a plan in place. And between shipping on hand in the Soviet Far East, and Lend-Lease craft from Alaska the USSR could probabaly have gotten a Corps sized force ashore, and told them to capture a port or die in the attempt.
Its very much something I wouldnt have wanted to be part of that is for sure. And Stalin's closest advisors knew it was both risky and not something the US would have been excited to see, but had the war dragged on into Fall of 1941 that opens up several other questions on if that restraint holds.