My dad's last name is cardoza, am i portuguese?

You can't go on your surname to find your ancestry, you need to research your own family history to find that out..........a z or an s can make a whole lot of difference between Spain and Portugal, however so can a simple spelling error...that is in the past many people didn't read and write, would say their names and someone else would write it down as to how it sounded to them, as they couldn't read and write and so the spelling of their name wasn't 'precious' to them, it could get written down differently each time..............however in your case you say you know you have Spanish ancestors so it is much more likely that it is Spanish...research your ancestry via family records and you will find out for sure.