We dont offer support for these types of modifications to Power Store.
It would take a lot of unsupported customization to add a new column to the products table for the different currency and have that used for only the .ca domain.
changing the way the currency is displayed on the page is also not supported, you would need to edit the code directly in to many places to list.
to add a menu item to the navigation, you would need to edit the webassist/plugins/main_menu/menu.php file.