Very good Dwayne. Let me tell you my experience. I was born in Spain. My father , and his father and grandparents are all from Puerto Rico. I live in Texas. My grandfather Luis M. Jusino (Sabana Grande) always told me that his family came from Corsica and he was pretty sure of it ("My grandfather told me" he used to say- His grandfather was born in 1825).
The last name is simple but complex. And I have tried to learn its real origin.
As a Spanish last name- There is no theory or facts that support it. The last time I checked (circa 1990), the only Jusino's born in Spain were my cousin and I, and we are both the children of Puerto Rico born fathers.
Dropping of a T? It was more common to change the first and last letters of a last name than dropping middle letters. Besides, Giusino, Giustino and Giustiniano also exist in Italian.
As a Corsican last name- This theory is widely is supported by Corsicans and Puerto Rican Corsicans. I think they could come from there but I do not think is an original Corsican last name but a variation of either a French or Italian (Genoa or Sicily) last name. See, in French there is Juseau and Juso (Man of the sea), Jusino could be a variation of that. In Italian there is Giusino, Giuso, Giusti, Giustino. Jusino could be a variation or adaptation of that. Also, a Corsican variation could be Ghjusino (Ex: Ghjuvan= John, Juan). Maybe that Gh was dropped when they moved to the Americas or by the French.
Just an example: I have cousins in Puerto Rico with the last name "Giuliani", and there are also "Juliani". As per those Juliani's some of them tell me that the change form GIUliani to Juliani was done in Corsica, others were told that the change was made in the Caribbean.
As a Sicilian last name- this theory is strong and does not preclude the Corsican connection. There used to be a lot of sailing in the Mediterranean. Giusino seems to be a logical beginning. Maybe they moved to Corsica where the last name adapted to either Jusino or Ghjusino this one with a latter change to Jusino.
As I have read, the 1600's-1800's were changing times, people moved a lot, sailed a lot. I have found records of Jusino's in New York, Hungary and Scotland. Not in Spain though. I remember in 1992, I went to a book fair in Spain and I saw a book on Puerto Rican immigration. The record showed an immigrant named Patrizio (with a Z) Jusino, as a land owner in Sabana Grande (1700's).
Let's say for a moment that they were originated in Sicily, moved to Corsica and then via Spain/Spanish Cédulas came to the Americas. Maybe they stopped at places like St. Marteen or other Caribbean islands, and then went to Puerto Rico and the US mainland, or the other way around, first Ellis Island and then Puerto Rico. It is hard to know.
My take is that we have a beautiful last name, pronounced wit heither an Spanish or an English "J", which I don't mind either way based on the origins. To know its origin, we would have to go back in time, descendant by descendant, until we get to the first one...