Preheat the oven to 350°F. Grease and flour an 18 x 13-inch half-sheet pan.
Put the first five ingredients in a bowl and whisk together until well incorporated. Set aside. Beat the oil and the sugars together until well blended. Add the eggs, one at a time, beating well after each addition. Add the pumpkin puree.
Stir the dry ingredients into the wet ingredients and add the toasted walnuts and raisins. Pour into the prepared pan and bake for approximately 25 minutes, or until a cake tester inserted into the middle of the cake comes out clean. Cool the cake in the
Beat the cream cheese and the butter together. Add the maple syrup and stir well. Mix in the confectioners' sugar until the frosting is the right consistency; adjust the consistency with more maple syrup or confectioners' sugar. Frost the cake and sprinkl