Using Ubercart with https protocol
If you care for SEO, consider using Metatag module:


  Meta tags have additional uses like the Open Graph Protocol used by Facebook, specifying the canonical location of content across multiple URLs or domains.


For Drupal 6 there is Nodewords module, that was inspiration for Metatag as far as I know.

To force https where you need it, use Secure Pages. You can check "Switch back to http pages when there are no matches" to make sure pages not required to use SSL will never actually use it - that way you save both server's CPU load (as encoding isn't free) and problems with duplicated content. It's pretty convenient, and a good first step, but it should not stop you from setting canonical, of course.