Make rhubarb simple syrup by combining sugar and water in a small saucepan, add sliced rhubarb, and mix over medium heat until sugar is dissolved. Allow to cool to room temperature and strain rhubarb out of the syrup.
Pour orange juice, simple syrup, and champagne into pitcher or serving vessel. Stir.
Add sliced oranges and/or frozen strawberries and chill for 1-4 hours before serving.
Just before serving, add club soda and stir. Enjoy with additional sliced fruit!
Recipe by SoFabFood at https://sofabfood.com/simple-spring-champagne-sangria/