1) Get a certain South American country to form a Free Trade and Immigration zone with its neighbors, which must include Ecuador, Colombia, Peru, Bolivia, as well as trying to get Chile and/or Argentina.
2) Once this alliance forms, use that country to house certain peoples from their neighbors in Development Areas. I was planning to establish said areas on the opposite side of the country where their borders exist. This way, while most people can move around, certain communities from other countries will be forced to integrate.
3) Use immigration and legislature to move in on the Panamanian border. My plan would entail to move +1,000,000 of the most poor/homeless people in the countries to the northern part of Panama, forcing Panama to enter the Union.
4) Also, I would try to have a strong relationship with Russia to ease the acquisition of Venezuela, I would do this via immigration. Immediately after Venezuela becomes ours, we would use our Russian diplomatic connections to help us move people in exchange for securing their interests. Any internal migration at this point will try to use parts of Argentina as resettlement zones.
5) Because Venezuela is more of a Caribbean nation than a South American one, we would push for the immigration of its people into the different countries of the union. Furthermore, we would repeat the same thing with those 3 small countries at the north-east of South America. We would use some of the Venezuelans that want to stay and send them to those 3 countries. Furthermore, we would send the populations of those 3 countries to push into Paraguay and Uruguay.
6) Once all of South America is one (Central America might also be needed), Brazil should also be targeted. We would send all sectarian/nationalist dissidents in the empty areas around Brazilia. Then disperse Brazilians on Central America to weaken them.
7) Start using the populations we don't want to start acquiring the Central American countries, mostly using the same method. At this point, we will call on Russia and even China if possible to help us migrate some people in Europe and South Africa. This is important because I'm planning to disperse the South African farmers in the empty farming areas of Central America. Furthermore, we will "try" to get Reparations from Europe because of Colonization or some other excuse.
8) Lobby in the US to make anti-hate legislature targeting WNs. Then work with the US to allow people marked as "potential terrorists" to be able to go to Central America with their weapons and property. This one move will ensure that you have men of fighting age and weapons in that region. Allow them to have land, while ensuring Central American governments favor us. Furthermore, South African farmers should be spread out evenly and also allow them to keep their weapons. This ensures any revolt in the region is stalled by the farmers.
9) Once we get to the Mexican border, we will "try" the same trick, but pressure Mexico and Canada to enter into a Confederation (which will make the US diplomatically trapped between the two). Once US is on that point, they will have no option but to enter into a formal pact between us (South American Union) or them (Mexico-Canada Confederation).
10) Once the pact is formed, we will push for immigration policies that "restrict" immigration between our countries BUT in actually it creates a pipeline to send any and all immigrants to the opposite side of their entry. This will diffuse any separatist sentiment on part of the immigrants as our governments grow stronger due to the immigration (economic and police expansion, to name some of the benefits).
11) Allow the people of our nations to drive the country together. The governments' jobs should be to form a continual and unified culture based on our history and rejecting the (((modern))) way things are done. We need to create our own history, cherish our own heroes, and have the same vision of the future. We might need another 9/11 to unify the country in tragedy, perhaps a terrorist group nukes some of the most degenerate cities in the continent.