Hi, are you logged in on eBay.ca? I think I remember that you can only use metric now when printing labels on the PayPal site. Canada Post uses metric, it is much more accurate anyway. It's been a long time since Canada changed over to metric from imperial. Hope this info is helpful.
edit:
Oops, sorry, didn't realize you are asking abou the shipping calculator. Can't help you there, I never use it.