My surname too is Alcantara (the Spanish form, with the accent). However, i am not from Spain or Portugal. I live in Australia, but i am originally from El Salvador, Central America. I have been interested in finding out the roots of my father's surname for a while now, and reading though the informations posted by Pedro Alcantara, i was able to learn about the origins of our surname.
If anyone would like to contact me, please email me at firstname.lastname@example.org