Start to Finish Time:
Combine blueberries, bananas, and ¾ cup cranberry juice in blender; blend 20 seconds. Pour mixture through a fine-mesh strainer, pressing with spatula, to remove skins.
Rinse blender; pour strained liquid back into blender with remaining cranberry juice and sugar. Blend another 20 seconds. Pour into molds; freeze at least 4 hours.