Preheat your oven to 350°F (175°C). Lightly grease a 9x13-inch baking pan with cooking spray and set it aside.
In a mixing bowl, combine the flour, baking powder, salt, granulated sugar, and cornstarch. Stir until well mixed. Create a well in the center and add the vanilla, eggs, milk, and melted butter. Whisk the mixture together until smooth and no lumps remain. Pour the batter evenly into the prepared baking pan.
Cut the peaches into bite-sized pieces and scatter them evenly over the batter in the pan.
In another bowl, beat the softened cream cheese, granulated sugar, and reserved peach juice together until the mixture is smooth and fluffy. Drop spoonfuls of this cream cheese mixture over the peaches and batter. Spread gently to form an even layer, allowing some of the peaches to peek through.
Generously sprinkle cinnamon and sugar over the cream cheese layer.
Bake in the preheated oven for 45-60 minutes, until the cake edges are golden brown and the cream cheese layer is slightly bubbling. The cake is done when the center is set and no longer jiggly. If needed, bake longer until the middle is fully set.
Serve warm or at room temperature for the best flavor.