| >allowing for the fact he has no idea about the specifics of the holiday*|
Actually, there isn't a whole lot of specifics. About the only thing you need to know is that Americans get together with extended family and traditionally eat turkey (since this was the food of choice at the first Thanksgiving feast by English settlers and Native Americans). If you've seen the first Spider-Man movie you've got the idea.
The Spider-Man balloon banner makes reference to a famous Thanksgiving day parade aired on U.S. TV which is basically a series of pop culture balloons. The only other tradition you might need to know about is that after eating, many people watch football (American football that is).
What Thanksgiving is like in Candada (which celebrates on a different day than in the U.S., about a month earlier) I have no idea. Maybe Cbasfrench can help with that one.