Place bacon in a large, deep skillet and cook over medium high heat until evenly brown. Drain, crumble and set aside - In a medium bowl, combine the broccoli, onion and raisins In a small bowl, whisk together the vinegar, sugar and mayonnaise and pour over broccoli mixture, and toss until well mixed; Refrigerate for at least two hours. Before serving, toss salad with crumbled bacon and sunflower seeds.