IMO Antonio Guiteras
https://en.wikipedia.org/wiki/Antonio_Guiteras is the key man in any "Trotskyist Cuva" scenario.
Trotskyists (such as Sandalio Junco and Eusebio Mujal) became quite important in Guiteras' "Joven Cuba"--though by doing so, they became non-Trotskyists in "orthodox" eyes. Guiteras himself was not a Trotskyist but some Trotskyists liked to think he was moving in their direction before his death. In 1962 Joseph Hansen referred to a report on Cuba which appeared in 1935 in the Americaan Trotskyist magazine *New International*:
"Of special interest in the radical movement at the time was the rapprochement between Antonio Guiteras, head of Young Cuba, and the Trotskyists. The report refers to this: 'Guiteras had a broader view than his successors. He had an international perspective for the Cuban revolution. To achieve this goal he had the intention of convening a continental congress in Mexico of all the parties of the Left and he insisted a good deal on inviting all the sections of the International Communist League [the Trotskyists] on the American continent, as he informed our party.'
"'But early in May, Guiteras was taken by surprise by the army near the town of Matanzas, just at the moment of embarking for Mexico. Together with the Venezuelan Colonel Carlos Aponte, he was assassinated.'
"'The death of Antonio Guiteras created a different situation on the Cuban political scene.'
"Today Antonio Guiteras, who might have developed into the Castro of the thirties, is revered as one of the martyrs of the Cuban Revolution. Rightly so, for it was the independent current represented by him and the Trotskyists and similar revolutionists in the thirties and preceding decades that finally produced a leadership capable of toppling the Batista dictatorship and winning the first great victory of socialism in Cuba."
https://www.marxists.org/archive/hansen/1962/10/hansenvhoy.htm
I did a "Guiteras lives" series in 2004 in soc.history.what-if called "Return of the Rebel." I hope to get back to it some day. (Maybe I drew too many parallels with Castro, but they are so striking it is impossible to ignore them--he had even planned an attack on the Moncada barracks!) In any event, seeing Guiteras evolve into a quasi-Trotskyist is easier than with Castro. By the time Castro took power in 1959 Cuban Trotskyism was very weak and had nothing to offer him, whereas the Communist PSP could offer him experienced cadres. (And of course Raul Castro and Che Guevara were strongly pro-Stalinist and anti-Trotskyist.) Furthermore, by 1959 the Soviet Union would be important in defending revolutionary Cuba against a hostile US, whereas in the 1930's there was little the USSR could do to help.
In OTL, incidentally, the Trotskyists who had joined "Joven Cuba" mostly went over to Grau's "Autenticos" after Guiteras' death. One of them, Eusebio Mujal, earned notoriety for his opportunism--originally he was a Communist, then a Trotskyist, then Secretary General of Joven Cuba, then an Autentico (Grau and Grau's then secretary of labor Prio assisted Mujal in taking the Cuban Workers Federation or CTC away from the Communists[1]), and finally Batista's man in organized labor in the 1950's...
[1] Amusingly, it was pressure from the US government that *delayed* this process! Lazaro Pena and his fellow Communists in the CTC had been so loyal to the wartime Great Alliance, so eager to make no-strike pledges, that the US government at first didn't want them replaced in 1944, as Grau already wanted to do...