1. Preheat oven to 425°F. Combine maple syrup, vinegar, 1/2 cup water, oil, salt, and cinnamon sticks in 13- x 9-inch baking dish. Add sweet potatoes, and stir to coat.
2. Cover dish tightly with foil, and bake 10 minutes. Uncover, and bake 30 to 35 minutes more, basting potatoes every 10 minutes with maple mixture, until maple mixture thickens and potatoes glisten and begin to brown. Remove from oven, season with salt and pepper (if desired), and stir in sunflower seeds.