I was in a competition this weekend with students from all of New England and Eastern Canada, at which no one was allowed to actually reveal where we were from (didn't want to bias the judges). I played, "Figure out where they're from by the accent," and I basically couldn't!
One girl from Ukraine but studying in North America was a particular challenge. She did say some "odd" words to my mind, but I put it on her being from Eastern Europe. Made more sense when I learned she was studying in Toronto on top of that. Her Canadian teammates' ways of speaking were not particularly pinnable to a specific area until I knew they were Canadian, too.