Fidel Castro had around 11 children but the Canadian prime minister was not one of them.
Justin Trudeau is a Canadian politician who has served as the 23rd prime minister of Canada since 2015. He was born on 25 December 1971 and grew up with the profound influence of his father, Pierre Elliott Trudeau, and his mother, Margaret Trudeau. Justin Trudeau's statement of 26 December 2016 praising Fidel sparked a controversy that he was the secret love child of Fidel Castro and Margaret Trudeau. Incidentally, Fidel, and Justin have a physical resemblance.
The Trudeaus were close to Fidel Castro and exchanged letters. However, no official meetings took place until 1976. Justin's mother, Margaret, was always under scrutiny by the press as she was the wife of prime minister. There is no evidence to support the notion that Margaret Trudeau met Castro before 1971. The timeline also supports that she gave birth to Justin just ten months after her wedding with Pierre, on Christmas Day in 1971.