Get archives as array

If you look at wp_get_archives() you will notice that the link is generated by get_archives_link(). That function supplies a filter that will allow you to replace the parens.

This is fairly crude but does work.

function archive_link_wpse_183665($link) {
  $pat="|\(([^)])\)</li>|";
  //   preg_match($pat,$link,$matches);
  //   var_dump($matches);

  $link = preg_replace($pat,'[$1]',$link);
  return $link;
}
add_filter( 'get_archives_link', 'archive_link_wpse_183665' );