The final episode of season 3 will be a one-hour special, but judging from the various reactions, it seems that rather than touching on the movie, the main story will move forward more directly (or the narrative will conclude).
That being said, I'd like to talk a bit about the 15-year lie (hopeful wish) that will surely be made into a movie.
There was some mention of the casting in the show, but as an anime-only viewer who hasn't finished reading the original manga, I'd like to predict the casting and indulge in my own self-satisfaction 😆
First, the ones that have already been decided...

Who were the fake cast members in 2015? (Just ramblings from an anime fan) No spoilers! | mentamago's post