Makes about 3 quarts
Combine lemon juice, sugar, orange juice, Grand Marnier, Triple Sec, and Cognac in a nonreactive bowl and stir until sugar is completely dissolved. Add Champagne and stir to combine. Cover and refrigerate until chilled, about 1 hour.
Pour into a decorative bowl or pitcher. Garnish with citrus slices and fresh strawberries. Serve in Champagne flutes, wineglasses, or punch cups.