Put the sugar and 1/4 cup water in a small saucepan and bring to a boil over high heat. Boil until the sugar dissolves, about 5 minutes. Transfer to a bowl or measuring cup and cool in the refrigerator.
Combine the cherry juice and half of the cooled simple syrup in a large pitcher. Add the cava and stir to combine. Taste and add more simple syrup if desired. Serve in chilled wine flutes.