In a large mixing bowl, mix together the broccoli, cheese, raisins, bacon, sunflower seeds, and onion.

Make the dressing: In a smaller bowl, mix together the mayo, sour cream, vinegar, sugar, and salt and pepper (to taste) until smooth.

Add the dressing to the broccoli mixture and toss until everything is well coated.

You can eat this immediately, but it's better if you let if chill in the refrigerator for about an hour before serving.