Preheat the oven to 350 degrees F (175 degrees C). Grease a 9x13-inch baking dish.
Cut bread into 1-inch cubes. Transfer to a baking sheet and spread in a single layer.
Toast in the preheated oven, stirring occasionally, until lightly browned, 8 to 10 minutes. Remove from the oven.
Beat sugar, butter, milk, and eggs in a large bowl until well combined. Stir in undrained pineapple and toasted bread; toss until coated. Pour mixture into the prepared baking dish.
Bake in the preheated oven until puffed and golden, about 45 minutes.