Grease and flour 2 round cake pans or a 9x13 baking pan. Bake cake according to package directions, substituting the 1 1/3 cup guava juice for the water called for. Allow to cool completely.
Meanwhile, in a mixing bowl, beat cream cheese with hand mixer until fluffy. Add sugar and vanilla and beat until completely mixed and smooth. Slowly fold in the Cool Whip, combined well. Refrigerate until ready to use.
In a medium saucepan, bring 1 1/2 cups guava juice and sugar to a boil.
Make a slurry out of the 1/4 cup cornstarch and the remaining 1/2 cup Guava juice. Remove guava juice from heat and stir in the cornstarch slurry. Add a few drops of red coloring, if needed. Return to heat and bring back to a boil for one minute. Allow this to cool completely.
To assemble cooled cake:
For a round layered cake; thickly ice the cake with of the cream cheese mixture in between the layers, leaving a well in the center of the layer. Pour some of the glaze in between the layers.
Top with the cake and repeat with cream cheese and then glaze the top of the cake with guava gel. Refrigerate until set before serving.
IF using a single layer 9x13 pan; ice the entire cake, pour some of the glaze over the center. Refrigerate until set before serving.