Very crowded. I highly recommend arriving at the gates 45-60 min before park opening. Use FP as much as possible. Also since Sunday is a Magic Morning day and Monday is not, I would recommend touring Adventureland, Frontierland, New Orleans Square, and Critter Country on Sunday. That leaves Toontown, Fantasyland, and Tomorrowland for Monday.
That's because assuming that you aren't staying at an onsite hotel, other guests will be allowed into the park to ride Fantasyland and some Tomorrowland rides because they will have Magic Mornings. So then when the park is open to everyone, steer clear from the rides that already have lines.