$marca_arg = isset($marca) && is_array($marca)
      ? $marca : [];

  foreach ($marcas_terms as $marca_term) {
    <a href="<?php echo (in_array($marca_term->slug, $marca_arg)) ?
     esc_url(remove_query_arg('marca')) : esc_url(add_query_arg('marca[]',
     "$marca_term->slug")); ?>" <?php echo (in_array($marca_term->slug,
     $marca_arg)) ? "class='selected'" : '' ?>><?php echo $marca_term->name;
    ?></a>
  }