Place bacon in a large skillet and cook over medium-high heat, turning occasionally, until evenly browned, about 10 minutes. Drain the bacon slices on paper towels and cool. Chop bacon.

Mix broccoli, bacon, red onion, and raisins in a bowl.

Whisk mayonnaise, sugar, and vinegar together in a bowl; stir dressing into broccoli mixture until evenly coated. Cover bowl and refrigerate for flavors to blend, about 1 hour. Sprinkle salad with sunflower seeds.