If you've selected that as one of the countries you ship to and added a shipping fee for the US, it will show on .com. If you do not include a shipping fee, it will not appear in Search south of the border.
Assuming you already have a metric tape measure and postal scale, you can use that tv show postal code '90210' and put the dimensions in metric (or you don't get an accurate reading) in here:
http://www.canadapost.ca/cpotools/apps/far/personal/findARate?execution=e1s1
With no $hipping to the US, it won't show. All that is explained here:
http://www2.ebay.com/aw/ca/201109221712382.html
