Whisk sugar, vinegar, salt, pepper, and olive oil together in a bowl until sugar is dissolved; set aside.
Toss kale, edamame, red onion, carrot, blueberries, dried cranberries, cashew pieces, and sunflower seeds together in a bowl. Pour about half the dressing over the mixture and toss to coat. Cover bowl with plastic wrap and refrigerate 4 to 6 hours. Serve remaining dressing on side.