Sprinkle 3 cups pecans evenly over a greased 15- x 10- x 1-inch jellyroll pan; set aside.
Cream butter in a large mixing bowl; gradually add sugar, beating well. Add eggs, one at a time, beating well after each addition. Stir in vanilla. Gradually add flour, stirring well. Spoon batter into pan.
Combine cherries, pineapple, citron, and remaining pecans in a large mixing bowl; mix well. Gently press candied fruit mixture into batter. Bake at 350° for 1 hour and 15 minutes or until lightly browned. Cool slightly; cut into 2- x 1-inch bars. Sprinkle rum over each bar.
Note: Store rum bars 2 to 3 weeks in airtight containers to mellow.