In a large bowl, whisk eggs, yogurt, sour cream, vanilla, and cinnamon together. Gradually whisk in the milk and maple syrup until blended.
Place half of the bread in a greased slow cooker, and layer with half the blueberries, half the cream cheese, and half the egg mixture. Repeat the layers. Cover and refrigerate overnight.
Remove from the refrigerator 30 minutes before cooking. Cook on low for 3-4 hours until a knife inserted near the center comes out clean.
In a small saucepan, mix the sugar and cornstarch together. Stir in the water until smooth. Stir in ΒΌ cup blueberries. Bring to a boil. Cook and stir until the berries pop, about 3 minutes. Remove from the heat. Stir in the butter, lemon juice, and remaining berries.
Serve the French toast warm with the blueberry syrup drizzled on top.