Place sugar, vanilla, cherries and 80ml of water in a small saucepan over medium heat. Cook, stirring until sugar dissolves. Then continue to cook without stirring until the cherries are tender and the syrup is thickened. Set aside to cool.
When mixture is cool, blend in a blender until smooth. Transfer to a jug and place in the fridge.
Wash out blender and then blend watermelon until smooth. Strain through a sieve to remove any solids. Place in a jug in fridge to chill.
When ready to serve divide cherry syrup between glasses. Add watermelon juice, orange liqueur and top with rosé and crushed ice.