Usually, American Airlines will send out their Boeing 737-800/MAX8s on hops between Miami, FL 
and the Caribbean 
you might have the occasional Airbus A319 or A321 on some routes but on the majority it will be some type of 737. Well I said majority because during some occasions like now, AA will fly some of their widebodies to and from the Caribbean from some of their various hubs. Back in 2021-2022 we say flights to Port-au-Prince, Haiti 
Montego Bay, Jamaica 
and Havana, Cuba 
be operated by Boeing 787-8 Dreamliners. And even after the MBJ and HAV routes have been downgraded and the PAP one suspended indefinitely, some routes still have them. American currently flies their Boeing 777-200ER on flights between MIA and San Juan, Puerto Rico 
daily and I’m pretty sure they also serve SJU with B772s from DFW more regularly than MIA.
Random Florida fact
Florida leads the US in terms of population of Puerto Ricans, they can be found all over the state but most commonly around the Orlando area
Origin: Miami Intl 
(MIA/KMIA)
Destination: Luis Muñoz Marin Intl (SJU/TJSJ)
Flight Time: 2:08
Boeing 777-200ER (American Airlines)
Server: Expert
American Airlines Boeing 777-200ER banking over the beautiful crystal blue waters 
of the Caribbean just slightly south of Nassau, Bahamas 
as she makes her way to SJU from MIA