According to the Italian Wikipedia, the proportions are 7.5 cl wine, 5 cl Select bitter, 2.5 cl sparkling water. I don't know where to get Select here in Switzerland, so I found it an inspiring idea to use Campari-style bitter instead, or simply Campari. Prepared like this, the drink reminds me a lot of the Negroni, just less strong and complex.
Yes, as per the recipe above, the classic proportions are 3:2:1.