We like the combination of nectarines, strawberries, and blueberries, but you can mix any summer fruit you like. Start with all ingredients chilled, or stop after step 1 and chill before adding the sparkling rosé.
Drop fresh fruit into a 3-qt. (or larger) glass pitcher or jar. Add Cointreau, then strawberry lemonade. Pour in dry rosé and stir gently with a long spoon.
Slowly pour in the sparkling rosé, taking care that the bubbles don't breach the rim of the pitcher or jar. Give the sangria another brief stir.
Spoon a little fruit into each glass. Pour sangria over fruit and garnish with a small mint sprig. Serve immediately.