Bring a large pot of lightly salted water to a boil. Add shrimp; cook 2 minutes or until no longer translucent. Transfer shrimp to a large colander with a large slotted spoon. Add scallops to boiling water; cook 1 to 2 minutes or until no longer translucent. Transfer scallops to colander with shrimp. Add calamari to boiling water; cook 30 seconds. Transfer calamari to colander with other seafood. Run cold water over seafood until no longer warm; drain well.
Combine cool seafood, fennel, and next 5 ingredients in a large bowl.
Combine lemon juice, vinegar, salt, and pepper in a small bowl with a wire whisk. Pour over seafood-vegetable mixture. Toss well to coat. Let stand at room temperature at least 15 minutes before serving.
Wine note: Pour a Champagne or sparkling wine, such as NV Laurent-Perrier, Brut L-P.