Preheat oven to 325° F. Grease and flour two 9-inch round cake pans.
For Cake: Combine flour, baking powder, pumpkin pie spice, baking soda, nutmeg and salt in small bowl. Beat sugar and butter in large mixer bowl until creamy. Add eggs; beat for 2 minutes. Beat in pumpkin, evaporated milk, water and vanilla extract. Gradually beat in flour mixture. Spread evenly into prepared cake pans.
Bake for 35 to 40 minutes or until wooden pick inserted in center comes out clean. Cool in pans on wire racks for 15 minutes; remove to wire racks to cool completely.
For Maple Frosting: Beat cream cheese, butter and powdered sugar in large mixer bowl until fluffy. Add maple flavoring; mix well.
To assemble: Cut each cake in half horizontally with long, serrated knife. Frost between layers and on top of cake, leaving sides unfrosted. Garnish with nuts, if desired.