Please read about Amazon Unified Marketplace Accounts here
To add an international account, add a company and then edit the country code and currency values (Settings > Add New Company). For example, for Amazon Canada you will need to set the country code to CA and the currency to CAD. The country code tells SellerCloud with which Amazon server to communicate.
MWS credentials for Amazon International Sites can be found at the following urls:
Product access keys for Amazon International sites:
Instructions on how to configure your Amazon account with SellerCloud can be found here