Cut the bacon into small pieces and cook over medium heat just until crisp; drain on paper towels.
Bring a large saucepan of salted water to a boil. Add the broccoli and blanch until bright green and slightly softened, about 3 minutes. Drain well, run under cold water to stop the cooking, and drain again.
In a mixing bowl, combine the mayonnaise, vinegar, onion, sugar and raisins. Add the broccoli and toss the coat with the dressing. Refrigerate for 1 hour.
Just before servings, fold in the sunflower kernels and the bacon pieces. Serve immediately.