To make the dressing: Mix the mayonnaise, sour cream, Dijon mustard, dill, and capers in a small bowl. Season, to taste, with salt, pepper, and hot sauce.
Layer the vegetables in a large glass bowl in the following order: romaine, tomatoes, carrots, celery, red pepper, and corn. Arrange overlapping slices of the cucumber on top. Spread the dressing over the cucumbers.
Cover tightly with plastic wrap and refrigerate until ready to serve, up to 8 hours. Just before serving, toss well.