MIAMI — The arrival of nearly 700 Haitians in a string of dramatic migrant landings near an exclusive wealthy enclave in the Upper Florida Keys over the past four months suggests that those behind the rise in Haitian boat migration are getting bolder, and using new trafficking routes to get to the United States. While smugglers are still ferrying desperate Haitians in overloaded, battered sailboats from Haiti, the clandestine voyages have become much better organized and sophisticated, U.S. and Haitian authorities say. The boats are now bigger and even engine-powered as opposed to sail, and sm…