I do not use canada post, but freeshipper is triggered by the conditions set in the functions_general.php file in the function zen_get_shipping_enabled ...

This checks the cart in various ways to see if the cart qualifies as being all Free Shipping such as:
1 all products are marked as Always Free Shipping
2 all products are Virtual products
3 total weight of the cart is 0

you might ask on the Canada Post thread about issues you are having with it ...