Preheat the oven to 350 degrees F. Lightly grease a 9X13-inch baking pan with cooking spray and set aside.
In a medium or large bowl, combine the flour, baking powder, salt, sugar and cornstarch. Blend. Make a well in the center and add the vanilla, eggs, milk and melted butter. Whisk together until well combined. Spread the batter evenly in the prepared pan.
Slice the peaches into bite-sized pieces, scattering them over the top of the batter evenly. In a medium bowl, beat the cream cheese, sugar and reserved peach juice together until light and creamy. Dollop the cream cheese mixture in tablespoon-sized spoonfuls over the top of the batter and peaches and then use a spatula to evenly spread together to form a creamy layer. It doesn't have to be perfect, just try to spread it as evenly over the top as possible (it's ok if peaches are peeking through in spots). Sprinkle the top of the cream cheese layer generously with cinnamon and sugar.
Bake for 45-60 minutes until the edges are puffed and golden and the cream cheese layer has bubbled slightly on top. This is a difficult cake to test for doneness because of the gooey cream cheese layer. If the middle is still jiggly, bake until it no longer jiggles and the cake batter layer is puffed and no longer runny. Serve warm or at room temperature.