I agree with Frank.

Unfortunately a quick imdb scan told me weeks or months earlier the performers in question that show up in the movie.

But if I hadn't known, it would have been a MUCH bigger and more pleasant surprise than the surprise towards the end of the movie. Especially since they aren't in the trailer (I don't think). The reveal at the end wasn't really that big a deal--to me, anyway. I almost wonder if they had others in mind first, but every other choice turned them down or had to drop out.

Mostly because one of the people in particular is FANTASTIC in the film, maybe giving the best performance of the film, and in general the best thing they've done since that other thing that most people remember them for.