Whisk together first 6 ingredients. Place bread cubes in a 13x9-in. or 3-quart baking dish coated with cooking spray. Pour egg mixture over top. Refrigerate, covered, 8 hours or overnight., Preheat oven to 350°. Remove berries from freezer and French toast from refrigerator and let stand while oven heats. Bake, covered, 30 minutes., In a small bowl, cut butter into brown sugar until crumbly. Top French toast with berries; sprinkle with brown sugar mixture. Bake, uncovered, until a knife inserted in the center comes out clean, 15-20 minutes. If desired, dust with confectioners' sugar and serve with syrup.