Soak chopped red onion in cold water while you prepare the rest of the salad.
Combine sour cream, maple syrup, salt, & pepper in a small bowl, and set aside. Place broccoli florets, pecans, and cranberries in a large bowl. Drain red onion, and add it to the bowl with the broccoli mixture. Drizzle the sour cream dressing over the veggies, and toss to mix the veggies so they are all covered with dressing. Cover and chill 1 hour before serving.