Guanciale is Italian cured pork cheek or jowl. It's traditionally used in classic pastas, like spaghetti all carbonara and bucatini all'amatriciana. Because it's largely fat, guanciale has a more seductive pork flavor and delicate texture than cured meat that comes from the belly (like pancetta, which is a common substitute, though the flavor isn't the same).
The distinctive taste of Cuban bread is due to the use of starter, which is made the day before and also very important the dough is enriched with lard. Yes, I said Lard from pork!! You can substitute with vegetable shortening such as Crisco if you prefer. However the taste the bread acquires and it's basic smoothness will only come with the use of lard. A little once in a while will not hurt. The authentic taste will only be achieved with Lard! Buen Appetito