If you go by cannnnon, 2nd ID and other units deployed to South Korea fend off the North Korean invasion and push the North Koreans all the way north into China, then link up with the Chinese army. Once nukes enter the picture, the US units are pushed back to Korea and basically end up where they started hunkered down behind the fortifications at the DMZ.
I don't have the US Vehicle Guide in front of me, but at least one of the US divisions, 2nd ID I think, is briefly cut off and comes under command of one of the Chinese armies. Then once the nukes start flying, makes it way back to ROK. One of the other divisions abandons its heavy equipment, and the 7th LID and 25th LID are basically overrun and reform in ROK with less that 1000 survivors.
so technically yes, US forces were deployed to China.
Cannnnon also has the British forces in Hong Kong forming the 6th ID and heading north. As far as other Asia-Pacific nations joining, in my campaign the Australians and Kiwis contribute smaller forces, battalion each.
Australians sending 2 divisions and New Zealand sending a division? not sure about that, the Aussies on this board would have better information but that is pretty much their entire army including reserves. Likewise with New Zealand, which is much smaller.
not sure about the Japanese sending ground forces either, too much bad feelings from the last war. Aircraft and naval forces, definitely, but not ground troops. not to mention the Japanese facing the Soviets over the Kuriles. V2 has the Soviets and Japanese fighting over the Kuriles and Sakhalin islands.
but if they work for your campaign, so be it.
I could see the Taiwanese intervening and sending an expeditionary force. I do that in my campaign.
By the OP's wording, I took it to mean a US unit sent to China before the hostilities between NATO and WP. Its possible that a US unit is sent to Hong Kong during that time since Hong Kong at that time was technically not "Chinese".
After hostilities, then who knows.