In order to automate Canada Post postal rate calculation and creation of postage you will need a Canada Post Merchant ID Number. Their service is completely free, and having a business account should also give you a lower shipping cost. Sadly, of all the realtime shipping methods, Canada Post's sign-up process is the longest and most complex.
Step 1: Setup a small business account
Call Canada Post’s Venture One Small Business Department: 1-877-262-5762
and select "Setup a Venture One account" from the audio menu. An agent will get some basic info and give you a very short questionnaire. They should then give you an Account # - be sure to write this down.
(Prompts: Dial 1 for English, # key to skip entering an account number, Dial 1 to set up a Venture One account)
Step 2: Visit Canada Post's Business website
Look for the "Does Your Employer Already Have an account?" and click the "Add Profile" button. Once there Create a User Name, Enter your Account # that you got in Step 1 and create a password. You can also fill out your profile and add a credit card # if you want.
Step 3: Request a Merchant ID Number for online shopping cart
Call Canada Post’s Sell Online Help Desk: 1-800-277-4799
(Prompts: 1 for English, Enter Account Number followed by the # key, follow prompt to talk with an operator)
Mention you are calling to setup a Sell Online Account so you can receive a Merchant ID# which you need for the online shopping cart module/plugin. They'll ask for your email address and then give you a user ID (usually something like CPC_YourCompanyName). They will also email you within a day a link to a web page where you will need to complete your account settings
Step 4: Complete your account settings
You'll receive a confirmation email from Sell Online Service confirming your Retailer ID and a link to your shipping profile, that will need to be updated. Login and add as much information as you can.
Once you've completed your steps you're ready to set up a realtime shipping method.