Welcome, both of you!
Brian, that's an adorable critter you've got there! As you get to know him better, you'll have a better idea of some of his more subtle personality traits, which will give you more of an idea of his ancestry. He's a good looking dog, though, whatever he came from! There's a thread posted with a link to a contest for the All American Mutt. You should enter your guy - he looks like a winner to me.