1/4 cup sugar
1/3 cup water
1/4 cup packed torn fresh mint leaves
8 sprigs fresh mint for garnish
1 (750 milliliter) bottle Sauvignon Blanc, chilled
1 cup fresh orange juice, chilled
1/2 cup Triple Sec or other orange-flavored liqueur
3 cups bite-size wedges of cantaloupe
1 1/2 cups bite-size wedges of seedless watermelon
Stir together sugar, water, and torn mint in a small saucepan. Bring to a simmer over low heat. Simmer 1 minute, then cool to room temperature, about 30 minutes. Strain syrup mixture through a fine-mesh sieve into a bowl, pushing on mint to extract as much liquid as possible. Discard mint leaves. Chill syrup until ready to use.
Stir together wine, orange juice, Triple Sec, and mint simple syrup in a pitcher or large bowl. Add cantaloupe and watermelon and chill at least 30 minutes and up to 4 hours.
Pour or ladle over ice, if desired, into 8 glasses and garnish each with a mint leaf or sprig.