Sprinkle both packets of gelatin in a 9-by-13-inch glass baking dish, and slowly stir in the boiling water. Cool to room temperature, then refrigerate just until gelatin begins to set, about 30 minutes — if the gelatin sets, you won't be able to stir in the goodies.
Meanwhile, in a medium bowl, combine the canned pineapple and its juice with the pecans and cranberry sauce. Add mixture to slightly thickened gelatin and stir until thoroughly combined. Return to refrigerator until firmly set. Cover with plastic wrap until ready to serve.