Sprinkle 3 cups pecans over a greased 15x10x1-in. baking pan.
Preheat oven to 350°. In a large bowl, cream butter and brown sugar until light and fluffy, 5-7 minutes. Add eggs, 1 at a time, beating well after each addition. Beat in vanilla. Gradually add flour to creamed mixture, beating well.
Spread batter into prepared pan. Combine candied fruit and remaining pecans. Spread fruit and pecans evenly over creamed mixture; press gently to help mixtures adhere. Bake until a toothpick inserted in centre comes out clean, about 1 hour. Sprinkle rum over the top; cool completely in pan on a wire rack. Cut into bars. Store in an airtight container.