override predefined countries

I have an address field, and I'd like to change the list of countries presented on the form. I couldn't find a hook in the documentation for this.

I found gform_predefined_choices filter but couldn't get it to fire and not even sure if it's what I want.

I tried:

add_filter("gform_predefined_choices", "ec_add_predefined_country");
function ec_add_predefined_country($choices)
{

	$choices['Countries'] = array('US', 'CA');

	return $choices;

}

Thanks!