Colin Peter was robbed and beaten on the beach while walking with his wife near the resort where they were staying last Thursday, said St. Lucia police.
Police also said Peter was hit on the back of the head with a piece of wood. His backpack, camera and wallet were stolen.
His son, Andrew Peter, said his father was taken to the Victoria hospital in critical condition.
Plans were being made to have him airlifted back to Canada, but he died Monday evening.
"We have a suspect which we are pursuing at this point in time, but the last update I had he was not apprehended as yet, but there is a suspect in mind. If the evidence adds up and he is connected to it. then he will be charged for murder in the first instance," said Vernon Francois, the commissioner of police in St.Lucia.
"We are profoundly sorry on St.Lucia for this. There is a great deal of sympathy both from the police department and the government of St.Lucia," said Francois.
Andrew Peter said the family views this an a crime of opportunity and harbours no bad feelings about St.Lucia.
Peter was in the country trying to research a branch of his family tree.
His wife, Gwen Peter, is still in St.Lucia. The rest of the immediate family is flying down for the cremation and a private ceremony. There will not be a traditional wake on P.E.I., but the family might have a memorial on the Island in the future.
Peter, owner of Montague Office Supplies in eastern P.E.I., had three adult children.
Canada's Department of Foreign Affairs hasn't commented on the death.