Yes it is Imitation . Not wood

sand, prime, paint.

Maybe caulk the seams too, since they are generally rough (caulking is hard on the fingers though). When I painted panelling it wasn't as shiney as yours. I used CIL primer and it adhered well - maybe test your primer first. See if you can scratch it off with your fingernail

You will need a quality BONDING primer( such as Coverstain) and you need to clean it first to remove any wax that might be there.