It's not that easy to just make a "second China". Because what made China China wasn't just cheap labor costs, it was the entire foundation built during the Mao era. Even India with its similarly large population size as the other comment here suggests can't just replace China overnight. If they could they would have done so already.

But India is pursuing a fundamentally different model of economic development and the US can't magically transform it with just their "carrot and stick method" that you mention. They would need not just to invest massively in a kind of Marshall plan style without immediate prospects for a return on that investment, which US capital is not going to be easily persuaded to do, but also change the entrenched oligarchic and political structures in India that stand in the way of China style industrial development.

And India is where the US's chances are highest. In South East Asia they stand even less of a chance, countries like Vietnam, Indonesia, Malaysia, they are much more highly integrated into China's economic orbit. And yes, the Philippines is a US neocolony that can serve as a military launchpad, but they definitely can't economically replace China. I think if the US imperialists really are thinking along the lines you laid out they are severely deluding themselves.

Do you have any idea how many more people China has compared to Vietnam? Land mass? Territorial waters? Natural resources?

That's not even considering how ideologically communist Vietnam is.

No, the only viable junior China is India right now.

But the US isn't looking for a junior China in the third world. They are looking to Canada, Mexico, and Europe as a portfolio play to replace China. They also plan to use South American third world countries for natural resources extraction. The US converting India to junior China while losing Brazil to the Chinese sphere of influence would still be devastating for the USA. The USA is looking for lebensraum.

There's no way they'll get that from any SE Asian country.

You should check how much of inputs in Vietnam comes from China (while yes, the majority of the outputs goes to the USA), and how much of their manufacturing force have Chinese companies at the core and Chinese supply lines. Also, how much they rely on China for required infrastructure, including how much electricity is currently supplied from Nanning.

Vietnam has potential, but that potential can only be capitalized if it aims to grow alongside a prosperous China.

The Philippines will need some type of revolution, drastically upgraded infrastructure, drastically improved education for its people. Their political structure is basically unchanged for centuries, with a couple of dynastic ruling families and as yet, a population unready for the structured existence of industrialization and manufacturing.