Getting Canada, Greenland and even Mexico added on to US would still not be sufficient to pass China economically though.
If US can get all Mexicans to USA GDP per capita levels, then they might approach China's size. But this would take a long time if even possible and be contingent on China not growing at all.
I think with US having friction with EU, being possibly forced to work on massive annexation projects and UN losing all power, it gives China a much better than ever ground condition to bring Asia under control.
Korea, Japan, the indochina peninsula and Indonesia, just some of them under total Chinese political/economic control will solve all future conceivable problems for Beijing. None of these countries are powerful, especially not the southeast Asian ones.
The armies of ASEAN still mostly consist of equipment that wouldn't be out of place in the Korean war. In the face of drone warfare, VLO platforms and massive airlift capability, it's hard to see anyone being able to fight back.
When US is goaded into multiple western civil conflicts and also provoked into a war with Iran, China should blitz through western colonies in Asia which will bring 500 million+ people into indirect control of China.