Preheat the oven to 375 degrees and grease a baking dish with melted butter or cooking spray.
Mix together the milk and the eggs in a large mixing bowl or a liquid measuring cup.
Add the melted butter to the milk mixture and mix well.
Add the sugars, vanilla, and cinnamon to the milk mixture and mix well until all the ingredients are combined and a smooth egg custard forms.
In an even layer, add the cubed bread to the prepared baking dish.
Sprinkle the blueberries over the bread.
Pour the egg custard over the bread cubes. Press the bread into the egg mixture to make sure all the bread is coated. Let that sit in the refrigerator for at least 30 minutes.
Bake the casserole for 30-35 minutes or until the top is golden brown. Let it cool slightly before serving.
