Lightly coat the inside of the slow cooker with cooking spray or butter. Add half the bread cubes in an even layer.
Scatter half the blueberries over the bread. Repeat with the remaining bread and blueberries to form a second layer.
In a mixing bowl, whisk together the eggs, milk, maple syrup, vanilla extract, cinnamon, and salt until smooth.
Pour the egg mixture evenly over the bread and blueberries. Press down gently with a spoon so the bread absorbs the liquid.
Cover and cook on low for 3 to 4 hours, until the center is set and no liquid egg remains.
Turn off the slow cooker and let the bake rest for 10 minutes before serving.