In the early 18th century, have the Spanish consolidate their holdings in Florida and win a few decisive battles to conquer Georgia. Expel the Protestants, convert the slaves to Catholicism, and start enticing Palatinate Germans, Spanish and Portuguese to migrate to the area to run the plantations. Have the Catholic Church convert and subdue the Amerindians of the interior. Have Florida and Georgia be a haven for runaway slaves. Have a mixed-race, freed, small farmer population grow in numbers and push west and north into the backwoods before the Scots-Irish get there.
The southeast extreme of the US remains Catholic and polyglot. Wars are fought by the US for access to New Orleans, but neither the port nor the Southeast region is ever conquered nor admitted into the union, for fear of papist/foreign/mixed-race "contamination." Instead, the British conquer the region sometime in the early 19th century, and it becomes an extension of their West Indies holdings. They ban slavery as in OTL in the 1830s. South Asian and Indonesian workers are brought in to work the cotton plantations, thus adding to the melting pot. By 1900 the religious demography is 70% Catholic, 10% Hindu, 5% other Christian, 5% Muslim, 1% Jewish, 9% other.