To prepare dressing, stir maple syrup into sour cream, mixing well. Cool.
Peel oranges and cut into 14-inch round slices.
Peel bananas and cut in half crosswise, then lengthwise; brush with lemon juice.
Arrange fruit in groups on lettuce-lined platter.
Place a bowl of Maple Cream Dressing in the middle.
Makes 4 to 6 servings.