So, how would a Fascist US deal with Latin America? Would it be conquered and annexed or would they opt for a "Pan-American Co-Prosperity Sphere" of compliant (and economically-exploited) puppets?
No annexations. That could mean too many Latin Americans would be able to try moving around, or the US population would expect the places to be given statehood. Much easier to let them rot. Perhaps some sort of Operation Condor early on? Though I suppose there aren't many communists to fight against... well, the US mostly kept to the Caribbean before the British selling so many of their stocks and holdings to the Americans gave the Yankees more power and influence in South America. I actually do wonder if the US would have better relatoins with the governments of Venezuela, Cuba, and Mexico than with those in Argentina, Chile, Brazil, and Uruguay. Depends on if there are fascists down there. If they are? Well, that might cause annoyance for Washington, as one thing that can be expected from Fascists is that they mostly want each other's land. Perhaps not a problem here when it comes to actual land, but the Spanish, Italian, and German populated states in the Southern Cone might use any anti-British propaganda they had at the beginning of this and move it over to being anti-American. They already had a bit of that at the time, though. Best hope for American interests is a Good Neighbor Policy, so that the Yanks can get several enormous countries on side with them against German and Japanese attempts to infiltrate South America.