you would need to add code to the confirm_cart page,af term the cart getContents function call, to set a session based on the shipping country. double check the checkout page for name of the shipping country form element.
for example, if it is named Country_2
the code to set the Session would be:
<?php
if(isset($_POST["Country_2"])) {
if(($_POST["Country_2"] == "US") || ($_POST["Country_2"] == "CA")) {
$_SESSION['shipregion'] = "North America";
} else {
$_SESSION['shipregion'] = "International";
}
}
?>
you can then add a trigger to the shipping rules for Based on session value:
if the session 'shipregion' has a value of 'North America'
for example.