COVER bottom of 13x9-inch dish with cake slices; set aside.
ADD boiling water to jelly powders in large bowl; stir 2 min. until completely dissolved. Add ice cubes; stir 3 to 5 min. or until ice is melted. Remove any unmelted ice. Stir in 1 cup strawberries; pour over cake. Refrigerate 15 min. Cover with Cool Whip.
REFRIGERATE 4 hours or until jelly is firm. Arrange remaining berries over dessert to resemble the Canadian flag.