How to pass argument in ctools_modal_form_wrapper?
You must use $form_state to do it. 

$form_state['build_info']['args'] = array($node);

function generate_tpls_callback($cid, $ajax) {
    if ($ajax) {
        ctools_include('ajax');
        ctools_include('modal');

        $form_state = array(
            'ajax' =&gt; TRUE,
            'title' =&gt; t('Display box to change title'),
            'cid' =&gt; $cid,
        );
        $form_state['build_info']['args'] = array($myvar);  //Check form below
        $output = ctools_modal_form_wrapper('myform', $form_state);
        if (!empty($form_state['ajax_commands'])) {
            $output = $form_state['ajax_commands'];
        }
        print ajax_render($output);
        drupal_exit();
    } else {
    }

}

function myform($form, &amp;$form_state, $myvar) {
...
}