I am using Commerce Shipping and I need to disable all countries, except for Canada and the US. How do I make it so only those two are available in the Shipping Info on checkout?
Easy (assuming Drupal commerce 7.1 in my testing) - you want to just navigate to
Admin > Store > Commerce Profiles > Profile Types > Manage Fields > [Your Address Field] > Edit
Under 'Available Countries', select the ones you want per the instructions 'If no countries are selected, all countries will be available.'
You may also refine the list of available countries that appear in the above-mentioned 'Available Countries' selection list (and any other country chooser in a Drupal 7.x site) with the countries module.