No, you would not want to use a power sander. I must ask why you would want to scrape the shingles. I would suggest a low pressure type of power washer. Note, I am not suggesting a pressure washer. A power washer should be able to remove the flaking paint without damaging the shingles. Go slow, be careful and keep the tip of the gun as far away as you can and still get the job done. Pausing too long in one spot with cedar will cause damage. Cedar absorbs the water quickly and will get soft quickly. This is why you do not want to spend too much time in one spot and damage the cedar.