Sweet and Sour Tofu Stir-Fry

2 cups broccoli florets
2 cups cauliflower florets
1 cup sliced carrots
1 tablespoon cornstarch
1/2 cup pineapple juice
1 tablespoon dark brown sugar
1/4 cup apple juice concentrate
1 tablespoon rice vinegar
2 tablespoons peanut oil
1 tablespoon finely chopped peeled ginger root
2 cloves garlic, finely chopped
1 jalape