Combine first 6 ingredients; set flour mixture aside. Combine pumpkin and applesauce; set aside.
Beat granulated sugar and margarine in a large bowl at medium speed of a mixer until well-blended (about 5 minutes).
Add egg whites and vanilla, beating well.
Add flour mixture to sugar mixture alternately with pumpkin mixture, beginning and ending with flour mixture.
Pour batter into a 12-cup Bundt pan coated with cooking spray. Bake at 350° for 50 minutes or until a wooden pick inserted in center comes out clean. Cool in pan 10 minutes; remove from pan.
Combine brown sugar, rum, and milk in a small saucepan, and cook over low heat until brown sugar dissolves. Remove sugar mixture from heat, and add powdered sugar, stirring with a whisk. Spoon glaze over warm cake.