How does your system deal with adding options for other postal service like FedEx?
It's not so much about how our system handles it as how Magento handles it. You will just enable our Canada Post module and the Magento Fedex module. The customer will then be presented with all of those options and will choose the cheapest / best option for them.
If there is any conflict between the modules, one or both of the modules will not work as expected.