He'd be up to no good as a spy but bear in mind that Walsingham didn't really set up his networks for Elizabeth until much later in the century. He would have no friends at all. It's unlikely that he would view the natives with much sympathy. The English of the period were extremely xenophobic. He could be a Catholic refugee from Edward VI's England if it's set that early or from Elizabeth's regime. It's possible that he could have been taken by slavers himself in North Africa and ended up in the New World via Spain or Portugal. There are some sources available for Barbary piracy. Check them out. The Darien Adventure did for Scotland's imperial ambitions in central America and buggered up Scotland's finances completely in the years running up to the Act of Union in 1707 but that's obviously much, much later than the period in which you're interested. I can't think of any earlier English settlements than those established in the early 17th century in North America. You may need to play a little too fast and loose with history for my taste to set one up earlier than that. Elizabeth didn't want to poke the Spanish with a stick by wandering around in their new back gardens. She would really rather not spend the money on the likely war which would arise since she was as tight as a frog's arse. Edward VI was more concerned with having a godly kingdom in England and Mary just wanted a child to secure her Catholic succession. She wouldn't have wanted to alienate her Spanish husband by sending out settlers or even really merchants to trade with the New World. Drake didn't complete his circumnavigation until 1580. That's worth bearing in mind. There may have been English sailors on other powers' ships but merchants are another matter.