Custom node routing

I have a product content type with alias: /products/headphone. This product page has two url variations:

• /products/headphone/wire
• /products/headphone/wireless

Both urls should point to the same node, however within preprocess function or twig, I should be able to capture which variation is loaded (wire|wireless)

I figured I should create a custom module and handle custom routing:

my_module.routing.yml:

my_module.modality:
  path: '/products/{product_slug}/{variation}'
  defaults:
    _controller: '\Drupal\my_module\Controller\ProductController::action'
  requirements:
    _permission: 'access content'
  options:
    parameters:
      product_slug:
        type: string
      variation:
        type: string

The part I'm struggling with is how to point the controller back to preprocess function:

function my_module_preprocess_node__product_page(array &$variables){
  // some preprocess stuff
}

This is what I currently have in my controller:

\Drupal\my_module\Controller\ProductController:action

public function action($program_slug, $variation) 
{
return [
        'template' => 'node--program_page',
        'variation' => $variation
      ];
 }