Hello,
Your issue can be a lot of things, something unpublished, an address not supported by CanadaPost, incorrect credentials, a postcode in an incorrect format for that CanadaPost API (which has been solved with the latest update).
I invite you to provide details regarding the issues I listed in my previous reply.
What is the address you're using in the checkout ?
Are you using a regular account or a guest account ?
Did you checked your credentials ?
Did you enable the debug mode and perform another test ?
Did you check that the plugin is right published ?
Regards,