I believe you can simply put CA and MX on vacation.

Thank you very much for the replies. Choosing vacation mode was exactly what Amazon recommended also. Below is there response.

Upon checking the information, you have signed up as North America Unified account.

With a North America Unified Account, you can conveniently switch in Seller Central between Amazon.com and Amazon.ca seller tools to list products and manage orders in both marketplaces.

Unfortunately, currently we do not have an option to close only CA and MX marketplace.

As an alternate option, you can change the listing status as inactive in vacation mode for those two marketplace, so you can sell only in US marketplace.

To view your current listings status in Seller Central, from the “Settings” drop-down menu select “Account Info.” The “Listing Status” box, will show the “Current Status of Listings” for your account.

To set your listings to inactive, follow these steps:

1. Click the “Going on a vacation?” link.
2. Select “Inactive” for each service and locale you want to deactivate and click the “Save” button.

Within 1 hour your open listings will be unavailable for sale on Amazon.com. When your listings status is “Inactive,” you will still be able to create and edit listings. Any additions and changes will be reflected on the website when you reactivate your listings.