Attach Canada Post SellOnline ship module to Wordpress cart

I want to sell a few items from a Wordpress site in Canada, and I need someone to integrate Canada Post's SellOnline shipping module with a Wordpress shopping cart. I have not yet chosen a cart, so you have some flexibility - if you have already done this before for a cart that works as a Wordpress plugin, we could use that one. Preferably one that is free or low priced. The Wordpress site will be hosted by [login to view URL] [login to view URL] I would like to do this relatively quickly, within the next few weeks. Because my budget is very small, this is probably only of interest to someone who has done this before and can use your previous knowledge/code. I would like to install this on a test site first, and then when everything is working, move it to my currently operating site.