Most of the 'Siberian' units were from the middle of Siberia. The forces that faced the Japanese were in what was called the "Soviet Far East". Stalin kept something in the order of 0.5-1m troops in the FE, just in case. Some of the better FE quality units were used in the west but only when new FE units had been raised. There was still a fair bit of armour kept there that was eventually used in August Storm (August '45), that is why some BT-7 and KV-1 were seen which had disappeared from the ETO order of battle 3 and 2 years before, respectively.
The Japanese got beaten in '38 and curb-stomped in '39 and had absolutely no wish to repeat that experience. The mineral, oil and gas treasures of Siberia were unknown at that time so the Japanese had no real reason other than 'honour' (IE revenge). The Asia mainland was the IJA's playground, SE Asia was the IJN's idea and SE Asia had what the Japanese lacked: oil, tin, rubber, etc. Exploiting China was Japan's economic Holy Grail and that turned out to be a poisoned chalice, consuming oil, steel and men that in turn triggered the Southern adventure.
Now I would not say that a Northern adventure was totally and utterly out of the question as the Japanese historically displayed suicidal national insanity in taking on the West, an act of utter strategic overreach and gross misreading of their opponents. However there was absolutely nothing to be gained from going North, so that would have been pointless, even in Japanese eyes. You can forget about "helping out Uncle Adolph" as the Germans and the Japanese, though allies, viewed each other as little more than useful barbarian monkeys, despite the officially enthusiastic words.
Japanese logistics were simply not up to the job of conquering the Soviet FE. The IJA was simply not capable of inflicting more than minor and local defeats on the Red Army. The IJN could have blockaded and shelled Vladivostok and shut down that route for lendlease, maybe even taken it, but that would have been the limit. Instead of a trail of starved corpses leading back from India, you would have had a long straggly picket fence of frozen Japanese marking the retreat from the Soviet FE. While Germany had some industrial leeway in mitigating Extreme Winter, after '41, the Japanese had much less production capacity and transport, so you would have EW in force every winter.
So overall, no reason, no capacity to succeed and would have been contained without much reduction of forces available against Hitler.