Query string state/province field
Since you have the jQuery tag, I assume you're open to a jQuery solution.

This StackOverflow question covers pulling a variable from a URL argument.
Then it's just a matter of identifying the CSS identifier of the field you want to fill (right-click, use &quot;Inspect Element&quot;) and referencing it.  E.g.:

var state = GetURLParameter('state');
$('#state_province_id-2').val(state);

The Select2 documentation suggests this should work on Select2 widgets as well.