Lightly mist a 9x13 baking dish with cooking spray and fill with bread cubes. In a large bowl, whisk together the egg whites, eggs, milk, sugar, cinnamon, vanilla and salt until combined. Pour egg mixture evenly over the bread cubes. Cover dish with aluminum foil and refrigerate overnight (or 8 hours).

Remove the frozen berries from the freezer 30 minutes before baking to let them defrost and pre-heat the oven to 350. Remove the baking dish from the refrigerator and bake it in the oven, covered, for 30 minutes.

Put the brown sugar in a small bowl and using two knives, cut the cold butter into the brown sugar until combined into a fine crumble. When the baking dish comes out of the oven, sprinkle the berries evenly over the top of the bread, followed by the brown sugar crumb topping. Return to the oven, uncovered, and bake for an additional 15-20 minutes.