No. Presa Canario and Spanish Mastiff are not the same breed. They are two different breeds from two different backgrounds. Presa Canario is a guardian and a descendant of catch dogs. Spanish Mastiff is a livestock guardian (LGD). Spanish Mastiff might be considered a far cousin of Perro de Ganado Majorero as Majoreros are indeed livestock guardians and not headers as some portray them. Perro de Ganado Majorero is a crucial part of a true Presa Canario playing a major role in bringing the breed from near extinction.
Confusion comes from some people Calling Presa Canario a Canary Island Mastiff. Thus some assume it can be also called Spanish not knowing Spanish Mastiff is a distinctive breed with it’s own history, and breed standard.
It also doesn’t help that some breeds do not carry a proper name suggesting they belong to the family of breeds they should be associated with. Spanish Mastiff, Perro de Ganado Majorero, and Pyrenean Mastiff are not true mastiff breeds but rather Livestock Guardian breeds in short LGD.
I attach here some photos of Presa Canario, Spanish Mastiff, and Perro Majorero so you can see the clear differences.