To prepare fruit, combine first 7 ingredients in a large bowl; toss gently. Cover and chill.
To prepare cake, coat a 12-cup tube pan with cooking spray, and dust with 2 tablespoons flour.
Lightly spoon remaining 3 cups flour into dry measuring cups; level with a knife.
Combine flour, poppy seeds, baking soda, and salt in a medium bowl, stirring with a whisk.
Place 1 3/4 cups sugar and butter in a large bowl; beat with a mixer at medium speed until well blended.
Add eggs, 1 at a time, beating well after each addition.
Combine buttermilk and 1/4 cup juice.
Add flour mixture to sugar mixture alternately with buttermilk mixture, beginning and ending with flour mixture. Spoon batter into prepared pan.
Bake at 350 for 43 minutes or until a wooden pick inserted in center comes out clean. Cool in pan 10 minutes on a wire rack; remove from pan. Cool completely on wire rack.