In a large bowl, whisk together the milk, chia seeds, maple syrup, cinnamon, and salt. Refrigerate while you make the fruit sauce.
In a large saucepan, combine the cranberries, raspberries, sugar, and vanilla with 3/4 cup water; bring to a boil over high heat, stirring to help the sugar dissolve. Simmer over medium heat until the berries start to burst and the sauce is thick, 10 to 15 minutes. Use a spoon to mash the berries.
Let fruit mixture cool slightly, and then spoon 1 to 2 Tbs. of sauce into each of 8 small glasses or jars and let cool to room temperature.
Ladle the chia pudding into the cups. Refrigerate the glasses and remaining sauce until the pudding is thick, at least 4 hours and up to 2 days. Just before serving, spoon the remaining sauce on top of the pudding.
Prep the pudding and sauce and refrigerate in separate bowls. Assemble and serve in the morning.