I can sometimes tell if an actor is Canadian by certain pronunciations, such as how they say tomorrow or sorry which differs from standard American accents, but not all have that distinction . I can usually tell when an actor is British and putting on an American accent if they slip up and add an ‘r’ to the end of a word or name that ends with an ‘a’. There are other instances where I hear that the pronunciation is not quite there. But I think you have to watch a lot of British tv and films and pay attention to those distinctions in order to notice them. I can’t remember exactly what phrases she said but, I did not know anything about the actress that was in Maze Runner until I noticed her accent come out and I googled her and sure enough she was British.