Preheat oven to 325°F (160°C). Grease and line with parchment, two 8-in. (20-cm) round cake pans. Prepare cake batter according to package directions. Divide batter evenly among the 2 prepared pans. Bake 30 min. until golden. Remove from oven and cool slightly on wire rack. While still warm, poke holes into cakes about 1 in. (2.5 cm) apart using the handle of a wooden spoon. Do not let the handle touch the bottoms of the cake pans. Cool completely.
Whisk jelly powder with 1/2 cup (125 mL) boiling water until dissolved. Immediately whisk in 1/4 cup (60 mL) cold water. Pour over cakes (holes and cake). Chill 6 hr. or overnight until gelatin is set.
To prevent cracking, bring cakes to room temperature before removing from pans (discarding parchment liners if using). Place cakes on wire racks.
In large bowl, whip cream with electric mixer to soft peaks then gradually beat in icing sugar until smooth and fluffy. Place first cake on large plate or platter. Spread icing on top before stacking second one. Ice top and sides of cake. Split maple leaf cookies to decorate cake, if desired. Chill 30 min. to firm up icing before serving.