Floating Cucumber, Tomato, and Onion Salad

8 cups peeled, thinly sliced cucumbers

1 large sweet onion, thinly sliced

1 tomato, seeded and chopped

1 ½ cups white sugar

1 cup distilled white vinegar

¼ cup balsamic vinegar

1 ½ tablespoons salt

1 teaspoon celery seed

Toss together the cucumbers, onion, and tomato in a large salad bowl. In a separate bowl, whisk together the sugar, white vinegar, balsamic vinegar, salt, and celery seed until the sugar has dissolved. Pour over the vegetables, toss again, and cover. Refrigerate for 12 hours or overnight before serving.