The USA relying on importing millions of Browns to make up for its low fertility rate versus China having demographic time bombs but mostly homogeneous Han Chinese.
China wins.
There's no scenario a country wins by importing millions of Brown Third Worlders.
See, Canada.
Vietnam's manufacturing is mostly low-end goods, it spurs economic growth, but it doesn't make them at all a powerhouse. China has upscaled to robotics, AI, and microchips.
You need to look at several factors, Vietnam scores low on economic complexity because the goods they produce are not highly specialized. On top of that, they don't have vast oil and mineral reserves to fall back on. There is no inidication or plans for Vietnam to upscale to humanoid robotics and nuclear technology.
I can talk more about this but its entirely out of topic. China will break the middle income trap, and become a high income global power, even though their country is ageing they've already caught up to the USA in economic complexity (technological know-how and sophistication).
Canada's future is a lot less bright than China, let's put it that way. Canada doesn't even have a humanoid robotics industry. East Asia (Japan, Korea, China) have all surpassed Canada technologically by miles. The USA and the UK are the only other countries that can compete with East Asia, but them bringing millions of Third World Browns is gonna backfire.
Again, so many factors to include, like culture. Importing millions of Browns from Third World cultures is a burden, technological advancement is in some ways indirectly tied to hygiene, sanitation, safety, and cultural sophistication. We're replacing low birth rates with Third World culture and people. That's a f*cking disaster. You ain't getting Naboo, you're gonna get Coruscant.