The Spanish or the English could never get any large scale settlement into Florida due to the susceptibility to disease in the swamps. While it is true that the ranchers who settled on dry land came down from Georgia, many of the citrus pioneers who came down prior to Governor Broward's decision to "re-route" Okeechobee and drain the everglades were from the north. It was really yankee citrus farmers and the original snowbirds who benefitted most from Flagler's railroad.
While it is true that much of the white proletariat that followed the railroad came from other southern states, they were always a minority on much of the east coast of Florida (and the Gulf from Sarasota south). Even a place like Tampa was more noteworthy for its Cuban, Italian, Jewish, Spanish, etc. population than its small population of "true southerners 100 years ago. In short, the only places in Florida that were truly culturally "southern" historically were the cattle counties in north and central Florida, and the panhandle. This is the source of the old joke that in Florida, you go north to go South, and south to go North.
good post
NautiNurse: Clemenza's post #54 may interest you...