The night before,spray a 9x13 baking pan with nonstick cooking spray. Add the bread cubes and 2 cups of the blueberries, toss together, and set aside.
In the bottom of a mixing bowl, use a wooden spoon/potato masher/fork to roughly mash the remaining 1 cup of berries. Add in the sugar and eggs, whisk together. Pour in the milk, vanilla and spices, whisk again.
Pour the egg mixture over the bread cubes evenly. Cover with plastic wrap and refrigerate until morning.
Preheat the oven to 350. Bake for 30 minutes, then uncover and bake for an additional 30 minutes.
Allow to cool slightly, then dust with powdered sugar and serve with maple syrup.