Place the rice and cinnamon stick into a bowl and cover with a few inches of water. Allow to soak for at least 4 hours or overnight.
Drain the excess water, and then transfer the rice and cinnamon stick to a blender. Add 2 cups of water. Blend until the rice is very finely ground and the liquid is a milky color.
Strain the mixture through a fine-mesh strainer into a bowl or large-mouthed pitcher. Stir in the coconut milk, maple syrup, and vanilla. You can thin the mixture with some additional water and/or coconut milk, if you like.
Divide ice cubes among glasses and pour the horchata over the ices. Sprinkle each glass with some ground cinnamon, and serve.