In a blender, puree mangoes, cantaloupe, maple syrup, water & lime juice until very smooth. Pour into a shallow pan & place in a freezer. When the sorbet begins to freeze around the edges, stir well. Continue stirring every hour for 2 or 3 hours, until the mixture has frozen solid. Cover & let sorbet coninue to freeze overnight.
Before serving, let the sorbet thaw for 10 minutes: cut into chunks, puree briefly in a blender then scoop into serving dishes. Garnish with mint leaves if desired.