Whisk together the eggs, milk, granulated sugar and cinnamon in a medium bowl and set aside.
Cut the bread on the bias into 1/2-inch thick slices, about 16 pieces total. Add the bread to a large resealable plastic bag, then pour in the egg mixture, seal the bag and turn several times to make sure all the bread pieces are coated.
Put the bag in a medium bowl and chill in the refrigerator for at least 4 hours and up to overnight.
One by one, remove the bread pieces from the egg mixture, allowing any excess liquid to drip away onto a large baking sheet fitted with a rack.
Melt 2 tablespoons butter in a large nonstick skillet pan over medium heat. When the butter is melted and starts to lightly bubble, add half of the bread pieces to the pan in a single layer. Cook until browned on the first side, 2 to 3 minutes. Flip and cook until lightly browned on the second side and cooked through, 2 to 3 minutes. Transfer to a large platter or baking sheet. Carefully wipe out the pan and repeat with the remaining butter and bread.
To serve, divide the French toast among plates. Dust with confectioners' sugar and top with the mixed berries. Serve immediately along with the maple syrup for drizzling.