WooCommerce - Move some countries at the top of country list

/**
 * Moves Canada and the US to the top of the list of countries available
 * in WooCommerce.
 *
 * @author Aelia <support@aelia.co>
 */
add_filter('woocommerce_countries', function($countries) {
  $countries = array(
    'CA' => $countries['CA'],
    'US' => $countries['US'],
  ) + $countries;
  return $countries;
}, 10, 1);