Will powdered sugar with cornstarch suffice as levening agent?

No, powdered sugar with cornstarch will not suffice as a leavening agent. Leavening agents, such as baking powder or baking soda, produce gas that causes dough to rise. Powdered sugar primarily serves as a sweetener and the cornstarch helps prevent clumping, but neither ingredient has the properties needed to create the necessary chemical reactions for leavening.