Open the immigration limits on the Philippines.
They have a struggling population of 95 million hardworking mostly social-Conservative people, and already the “overseas workforce” of their population is a big part of their economy.
Philippino farm workers (would all speak English already) would either go back and forth as “temporary” workers, or become loyal Americans, but would not be, at any time, a nationalist fifth column of a next door neighbor.
Caribbean workers would also fit the bill. Most of the farm workers in Southern Ontario hail from that part of the world and many have been doing it for decades, returning home each winter.