In a large bowl, mix the cold white rice, drained crushed pineapple, powdered sugar, and miniature marshmallows.
In a separate bowl, whip the heavy cream with sugar and vanilla until stiff peaks form. Gently fold the whipped cream into the rice mixture until evenly combined.
Cover the bowl and chill in the refrigerator for at least 2 hours to allow the flavors to blend. Before serving, garnish with maraschino cherries if desired.