Start by washing the broccoli and cauliflower florets thoroughly under cold running water. Drain them well.
Chop the broccoli and cauliflower into bite-sized pieces and place them in a large mixing bowl.
Add the finely chopped red onion, raisins, sunflower seeds, and crispy bacon bits (if using) to the bowl.
In a separate bowl, prepare the dressing by whisking together the mayonnaise, white sugar, apple cider vinegar, salt, and pepper until smooth.
Pour the dressing over the vegetables and toss everything together until the veggies are well coated.
Let the salad chill in the refrigerator for at least 30 minutes to allow the flavors to meld.
Once chilled, transfer the salad to a serving platter or bowl.