MAKE AHEAD: In the small bowl, dissolve the sugar in the pomegranate juice. Store with the prepared pineapple, pomegranate seeds, and sliced oranges in the refrigerator for up to one day ahead.
SERVE: In the punch bowl, stir the sweetened pomegranate juice together with the sparkling wine and Reisling or Moscato wine. Add the orange slices, diced pineapple and pomegranate seeds. Serve the punch in stemmed glasses, adding ice cubes if desired.