Preheat oven to 350° degrees F. Liberally grease a 13x9 light metal rectangular baking pan with cooking spray. Set aside.
In a large bowl of a stand mixer, cream together the granulated sugar, pumpkin puree, oil, eggs, and vanilla extract with the paddle attachment on low speed until just combined, about 30 seconds. In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and spices. Gradually add the flour mixture to the pumpkin mixture until fully combined and batter is smooth and cohesive. Pour the batter evenly into the prepared pan and smooth out the top.
Bake for 25-30 minutes or until a toothpick or cake tester inserted in the middle comes out clean. Let cool for 15 minutes. While cake briefly cools, in a medium bowl, whisk together the heavy whipping cream, evaporated milk and sweetened condensed milk until combined; set aside.
Poke holes all over the warm cake using a skewer or dowel or if you don't have either, the handle of a wooden spoon or a knife's tip. Pour the milk mixture evenly over the cake, using all of the milk mixture. It will seem like a LOT of milk, but bear in mind that the cake will gradually soak up the mixture overnight in the fridge. Cover the cake and refrigerate 8 hours or overnight.
Just before serving, make the whipped cream frosting. In the bowl of a stand mixer, whip together the heavy whipping cream and confectioners' sugar until stiff peaks form, about 5-7 minutes. Spread the whipped cream evenly over the cake. Dust with ground cinnamon, if using. Store the cake in the fridge, covered.