You may want to try one of these tricks to keep your apples from turning brown.
Dice your apples and mix them with the mayonnaise, sour cream or whatever dressing you plan to use in your Waldorf salad, then add your celery, walnuts, raisins, or whatever other garnish and flavoring you wish on the day of the banquet. The oil and acids in the dressing will prevent the oxidation that causes the apples to brown. Make sure they are well coated and cover tightly with plastic wrap pressing onto the surface of the apples to keep out as much air as possible.
The other method you may try is to find some powdered Vitamin C (ascorbic acid) or citric acid (also known as Fruit Fresh TM), mix it with water and spray onto your apples, coating thoroughly. Tightly lay them out in pans (hotel pans or sheet pans will do). Soak clean bar towels with the solution and cover the apples with the towels. Then wrap tightly with plastic wrap.
I believe submerging them in water will end up making them very soggy as well as leach out much of the apple's flavor.
