Preheat the oven to 400 degrees. Arrange 8 slices of bread in the bottom of a 9-by-13-inch baking dish, squishing slices together to make one layer. Sprinkle the blueberries and peaches on top.
In a medium bowl, whisk together the milk, egg substitute, granulated sugar, cinnamon, and vanilla extract. Pour half of the milk mixture over fruit. Top with the remaining 8 slices of bread. Pour remaining milk mixture over bread. Using a spatula, press top layer of bread slices down to saturate with milk mixture.
Cover dish with aluminum foil and bake for 20 minutes. Uncover dish and bake until egg mixture is set and top is golden brown, about 10 minutes more. Cool slightly before sifting powdered sugar on top. Slice into 8 pieces and serve.