Always be Scanning randomly reverse searches the Amazon catalog for potential OA deals from TA retail sites. ABS is NOT added to your monthly minutes.
The ASIN's that are searched for you are different at the time of searching for other members, so your list will be different from other people. The items are removed after 28 days so if there is a deal that you want to save, you should move it to a saved folder.
Always be Scanning will work for the countries that your MWS keys work for so the US keys also work for Canada. It is completely random and there is not a way to change this.
If you don't wish to see results from any Amazon country, other than your specific country, you could use select the country that you would like to see here: http://prntscr.com/rvx47h