Son accidentally painted the new cedar shake! How to remove it

The paint stripper could be helpful but there is no guarantee, especially after you have sanded it quite a bit already. The stripper may get down into the porous parts of the wood and congeal the paint so as to make it come out. I would say that it is certainly worth a try in a small area to see if it helps. You'll know in short order if it would be worth the effort to go over the whole surface with the stripper. I give it a maybe 20 to 30% chance of making some difference.

If you do take on using the stripper....

• move the table to a very well ventilated area with no open flames or pilot lights
• wear good quality rubber gloves that extend well up over your wrists
• make sure to wear clothing that covers bare skin where ever the stripper could splash
• wear eye protection
• use care with disposal of the paper towels, rags and steel wool that you use with the stripper

Just to comment on your sanding effort. You did not specify how big the table is but 40 minutes of sanding with a small orbital sander using 60 grit paper over a large area is not really that much sanding. You have come this far so you may want to give it another go at further sanding. Do change your paper often as this can make a huge difference on how well the paper removes the wood. Also note that after sanding with 60 grit paper so much you will need to sand it with successively finer grits all the way to 220 or finer to get the surface in excellent shape for your poly finish.

I have two small areas of solid cedar. I used a natural/brown stain and a sealer. It had to be resealed every 3 years to look good , every 5 years just to keep it from bleaching. The same time I built a shed with cedar plywood and painted it ; it is still good after 15 years.