Melt 2 tablespoons butter in large pot over medium heat. Add onion and sauté until just tender, about 8 minutes. Stir in 1 tablespoon butter. Add carrots and sauté until coated with butter, about 1 minute. Stir in remaining 1 tablespoon butter. Add squash and sauté until beginning to soften, about 8 minutes. Pour orange juice over vegetables. Cover and simmer until vegetables are soft, about 25 minutes. Uncover and simmer until all liquid evaporates, about 5 minutes. Stir in maple syrup. Cool slightly. Working in batches, puree mixture in processor until smooth. Season to taste with salt and pepper. Transfer to serving bowl. (Can be made 2 days ahead. Cover and refrigerate. Stir over medium heat to rewarm.)
