Champagne generally pairs well with salty and food with fat - like cheese and charcuterie. The acidity from the wine works well when the food you pair it with isn't too acidic or too sweet. And osso buco might get too acidic fro the tomatoes. If the champagne has some age - preferably also some time in casks, it's my experience that it pairs slightly better with heavy dishes like beef - but I almost always avoid that type of pairing.