Translating (WooCommerce) placeholder text

You can filter gettext:

add_filter( 'gettext', function( $translation, $text, $domain ) 
{
    if ( 'woocommerce' === $domain and 'Select a state…' === $text )
        return 'Select a province…';

    return $translation;
}, 10, 3 );

Note the 3 as last parameter. This ensures you get all three variables passed, so you can replace exactly the text you are looking for.