If you want all of the paint removed then using a chemical paint stripper is one option. Another option is using an infrared paint stripper. Both will be a lot of work.
This type of siding can't be sanded, but I do have a couple of ideas that might help if combined with the paint stripper. Using a wire brush is a good method for removing the loosened paint. This is a bit labor intensive. To reduce the labor and speed things up you can use a wire brush attachment for a drill. This could be a good option. Be careful the wire brush can cause damage to the siding.
Apply more stripper to the areas where the paint has filled the groves and use a wire brush or nylon scrub brush to get the paint out of the grooves. Trying to provide a similar texture over this isn't a good idea.