The only reason the USSR became as powerful as it was was because of all the weapons and financial support America gave Russia, since Russia was an ally as well. Communism really sucked so I doubt it was enough alone to make Russia a superpower.
About Japan -- I don't think America would have such an easy time beating them. Nuclear power wouldn't come as soon, since the discovery of atomic bombs came mostly from German Jews who were forced to migrate to America; Albert Einstein, for example. With no Hitler to kill them, they'd most likely stay in now either a fascist or communist Germany, and God knows where the plans for a hydrogen bomb will end up.
Thus, with the absence of nuclear power, it's most likely that the US would carry on with Operation Downfall and invade Japan with a full-scale invading force. This would have been the largest amphibious operation in world history, and one of the bloodiest.
As for Korea, it would probably remain with Japan if Japan were to surrender. If not, it would most likely be ceded to America. China would still be communist, and Japan capitalist, with both of them becoming very powerful countries in the present day.
China benefited from German cooperation even before the Sino-Japanese war. In fact, if it weren't for the Japanese insistence that Germany stop supporting China (which occured in 1941, a whole 4 years after Japan had invaded China) the Chinese would be much better prepared to resist Japan. Also was the fact that Japan's war in China was unsustainable to begin with. And again, the US in our own historical timeline prioritized the war in Europe over the Pacific.
I doubt that China would go communist. Both the Americans and the Germans supported the Nationalist government. If the Japanese are kicked out of China sooner, then the CCP wouldn't have so readily gained power as they did. What you end up with in China is a US-friendly, capitalist-friendly Nationalist government. Also this means no Civil War, so China begins reconstructing in the mid 1940's instead of towards the early 1950's.
I think it would be highly disingenuous if the Americans return Korea to Japan, but it may be the case that Japan negotiates a surrender since their adventure in the Pacific comes to an early halt. The US doesn't want to invade Japan because it would kill millions, but the Japanese aspirations in the Pacific are finished. Without the bomb, I'm not too sure what would happen.
Would the US invade? Like you said, projections had US casualties in the hundred thousand, upwards of a million, not to leave out Japanese civilian deaths. The US can continue bombing Japan to the Stone Age, as this would alleviate US casualties. I don't think the US would be so pressured to sweep Japan quickly without a strong Soviet Union, so they could drag out the war. That might consequently make the Japanese more sympathetic to the Communists though, so you might end up with a reverse of what happens in history: a capitalist US-friendly China and a communist Japan.
What I think is most likely given this scenario is that Japan ends up negotiating an armistice, since their Pacific hegemony is now a pipe dream, Japan would prefer anything to Communism, and since they actually have something on the bargaining table (allowing the US to avoid a million-casualty invasion). Would Japan go full on peace? That would require a surrender. If the Japanese don't surrender and just go along with an armistice several things can happen. 1) The Soviet threat beckons both US and Japan to put aside their differences 2) Japan goes back to being a hermit state, somewhat like North Korea vs. South Korea, but even more effective since Japan's an island.
In scenario 2 the Japanese government would probably end up collapsing, and who knows what happens then.
In scenario 1 you'd have China, Korea and Japan under a US hegemony. Perhaps there'd be more of a united East Asia and a disunited Europe, very much the opposite of what happened in history.
EDIT: Also I'm not sure why you think Lend-Lease turned the Soviet Union into a superpower. Lend-Lease was just military support. That's all it was. It's like saying that Chinese support for North Korea during the Korean War turned the North Koreans into a superpower. American military support may have helped the Soviet Union defeat the Germans faster, but that's a separate issue to whether the Soviet Union had superpower status to begin with (which they did, with a large population, wealth of resources, Communism being attractive in many European countries, as well as being technologically advanced in the military realm).
