Make a simple syrup: Add the sugar and 1 cup water to a small saucepan and heat over low heat until the sugar is dissolved. Transfer to a container and allow to cool completely in the fridge, about 45 minutes.
Add the strawberries and lemon juice to a blender with the cold simple syrup; blend until smooth. Strain through a fine-mesh strainer to remove the seeds. Transfer to a pitcher and chill until ready to use.
To serve, add about 2 tablespoons of the strawberry puree to a champagne flute and top off with the chilled rose.