In a blender, combine the cherries, 1 cup pineapple, and juice. Cover and blend until smooth. Divide among 8 3-ounce plastic or paper cups. Cover with foil, make a slit in each with a knife, and insert a wooden pop stick. Freeze for 1 to 2 hours or until just firm. Remove from freezer; uncover. Top each with pineapple rings, cutting to fit as necessary. Cover and freezer until firm, about 2 to 3 hours.