Combine first 4 ingredients in a large bowl. Stir together eggs, oil, and buttermilk. Add oil mixture to flour mixture, stirring just until dry ingredients are moistened. Stir in banana and next 3 ingredients.
Drain pineapple, reserving 2 tablespoons liquid. Gently press pineapple and maraschino cherries between layers of paper towels. Chop cherries. Stir pineapple and cherries into banana mixture. Spoon into a greased and floured 10-inch tube pan.
Bake at 350° for 1 hour or until a wooden pick inserted in center comes out clean. Cool in pan on a wire rack 10 to 15 minutes; remove from pan, and cool on wire rack.
Beat cream cheese at medium speed with an electric mixer until smooth. Gradually add powdered sugar, beating at low speed until blended. Stir in reserved pineapple juice. Pour over cake; garnish, if desired.