Place carrots in a steamer basket; place in a small saucepan over 1 in. of water. Bring to a boil; cover and steam for 7-10 minutes or until crisp-tender. Rinse in cold water.
In a small bowl, combine the carrots, celery and onion. In another bowl, combine the mayonnaise, vinegar, sugar, garlic salt and pepper. Add to carrot mixture and stir gently to coat. Cover and refrigerate for at least 2 hours. Serve with a slotted spoon.