To use Canada Post's Sell Online^TM Shipping Module in Virtuemart you will need a Canada Post Merchant ID.  Here are the steps to obtain one.

First, sign up with Canada Post for a VentureOne Preferred Small Business Client account (it's free).

Once you have your VentureOne account #, send an e-mail to sellonline@canadapost.ca, requesting your account be registered on the Sell Online Server.  Be sure to include the following fields with your relevant information filled out afterwards:

CUSTOMER / VENTURE ONE NUMBER:
COMPANY NAME:
ADDRESS:
CITY:
PROVINCE:
POSTAL CODE :
MAIN CONTACT:
TELEPHONE NUMBER:

The sellonline@canadapost.ca e-mail appears to be managed manually by a human, so it may be a business day or so (based on Cybersalt's experience) before you receive an e-mail back with your Retailer ID for the Sell Online server.  That e-mail will also contain instructions for setting up the rest of your shipping profile with Canada Post.