Pick over the blueberries and remove the stems. Rinse well, place in a heavy large saucepan, and stir in 1/4 cup water and the sugar. Bring to a boil and cook, uncovered, until the berries are slightly softened and the juices are released, about 10 minutes. Stir gently from time to time.
Remove from the heat, cool slightly, and stir in the lemon juice.
Spread the butter on the bread slices and sprinkle with the cinnamon. Line the bottom of an 8 1/2 by 4 1/2 by 2 1/2-inch loaf pan with some of the bread slices, trimming to form a tight fit.
Spread 1/3 of the berries and juice evenly over the bread. Repeat to make 3 layers in all.
Refrigerate for 6 to 8 hours. Spoon onto plates and serve with vanilla ice cream or whipped cream.
