What if, in September of 1939, when Japan threatened to withdraw their ambassador and break off relations with Germany becasue of the Molotov-Ribbentrop Pact violating prior anti-soviet plans between Germany and Japan, Hitler decided to accept Ribbentrop's suggestion and reveal the plans for Operation Barbarossa to Hiroshi Ōshima and the Japanese High Command.
Knowing that the Germans had no intention of keeping their treaty with Russia, the Japanese would stick to the original Imperial Defence Plan of 1936, where Japan would not attack the US and rely on American neutrality, while invading Russia to supply their oil needs.
The plan they almost launched in OTL in July of 1941 was called Kantokuen. ITTL, they would have been firmly set on this plan since 1939, but would a Japanese invasion of Russia be successful, assuming that the USA remains neutral?
Also, irregardless of the Japanese success in their own war objectives, would forcing the USSR into a two front war improve German success on the Eastern Front?