In North America, is it culturally accepted that everyone knows who else is going to be at a meeting, or should one not be surprised if some people they did not think were going to be there arrive? I'm not talking about special circumstances (e.g. "I was in the office today and noticed there was this meeting I should go to") and not talking about meetings so large it's impossible to say who will be there. For example, if you schedule a meeting with one other person and it turns out there is a third person at the meeting, is that "unprofessional" (for lack of a better word)? Let me know if the question doesn't make sense.
EDIT: I was talking about internal. I had a problem working with some people so one person asked me to come to have a meeting with them. When I arrived another person was there that I did not expect to be there. But from the comments, it depends what type of meeting whether or not it's customary to tell people who will be there?