I'm not sure why you think so
The DPRK is there and it certainly won't be in the KMT's sphere.
South Korea is a US puppet and it doesn't have a reason to become a puppet of China, there probably would be some ties but nothing crazy.
North Vietnam is an enemy of China due to its Communist nature.
Laos, Cambodia and South Vietnam would be affected by TTL's Vietnam war and wouldn't be its puppets, they would be at best allies.
Burma doesn't have a reason to be a Chinese puppet.
France who has a much, much better army than the Chinese failed to take over Indochina so the Chinese managing to do so is ASB.
I think it's very hard because you have to fix a lot of Nationalist China's massive prewar problems, but assuming that they get their game in order, you can avoid a bunch of the conditions obtaining in OTL 1945.
Stuff like:
-- No North Korea due to changes in the overall China front leading to possibilities like no Soviet invasion of Manchuria, different negotiation results at Yalta.
-- Likely no South Korea either due to America seeing TTL's stronger China and the State Department just putting all of Korea under ROC purview.
-- Stronger Chinese military and proximity to Indochina facilitating their walking over the border, accepting Japanese surrender at Hanoi, and setting up bases in Vietnam.
-- Different outcome of negotiations leading to France accepting existence of independent, loosely China-aligned Indochina.
-- Vastly more competent KMT setting up friendly independent govt in Indochina/Vietnam, sideling or co-opting Vietminh. Insurgency avoided.
The more things are changed before and during the war, the greater the possibilities after the war. The challenge is setting up the earlier changes and progression of events to be realistic.