Actually Carl, Big commerce should have rel=canonical automatically formed but unfortunately the automatically generated rel=canonical has errors.

For example:

Pagination issues.

For page 2 the rel canonical it generates points to page 2 rather than page 1(which is the main page)

http://www.troisfemmesboutique.com/brands/Ya-Los-Angeles.html - this is the main page

http://www.troisfemmesboutique.com/brands/Ya-Los-Angeles.html?page=2&sort=featured - this is page 2 (check the rel=canonical for this page, you will know what I mean)

And if you add content on the main page, it duplicates it to the inside pages too. So rel=canonical would be perfect in this circumstances but you can only do so much with big commerce.

You can either hard code to fix this issue or just use robots.txt to disallow sorts!

Hope this helps.