Here is what Google emailed me, as far as their take on why purchases through cartmanager are not alllowing Canadian buyers:
I understand that your customer is having difficulty completing a
purchase. How did you request payment from your customer? The XML and HTML APIs automatically limit shipping to the country the account was
created in unless specifically stated otherwise. You could add a
<world-area\> or <allowed-area><country-code> tag into the API buttons to allow for international customers. Or you could send an email invoice
which should have no restrictions on shipping areas. For more information
on international shipping, please take a look at this tutorial:
Google Checkout: Merchant Help Center - How can I implement international shipping and taxes with the HTML API?
I passed this along to cartmanager, waiting.
