Place croissants and berries in a greased 8-in. square baking dish. In a medium bowl, beat cream cheese until smooth. Beat in milk, sugar, eggs and vanilla until blended; pour over croissants. Refrigerate, covered, overnight., Preheat oven to 350°. Remove casserole from refrigerator while oven heats. Bake, covered, 30 minutes. Bake, uncovered, until puffed and golden and a knife inserted in the center comes out clean, 15-20 minutes. Let stand 5-10 minutes before serving. If desired, serve with syrup.