In 1-quart saucepan, mix sugar, orange peel, orange juice and cornstarch. Heat to boiling over medium heat, stirring occasionally. Reduce heat to low; simmer uncovered about 8 minutes, stirring frequently, until sugar has dissolved and syrup has thickened. Stir in sliced mint. Cover; refrigerate at least 30 minutes, stirring occasionally.
Meanwhile, cut honeydew melon in half; remove and discard seeds. With melon baller, scoop out melon into balls; place in medium bowl. Cut cantaloupe in half; remove and discard seeds. Remove rind; cut cantaloupe into 1-inch-thick wedges. Arrange cantaloupe on serving platter.
Gently toss melon balls with cooled syrup. To serve, spoon melon balls on top and around cantaloupe; drizzle with remaining syrup. Garnish with mint sprigs.