The rules are the rules and i don't mean to be a jerk, but you "gambled" on the rules and you got burned. It sucks, but its the truth. Did the buyer receive the card or not? Its really anyone's guess, but when you see a brand new Ebay account buying from you (especially on a $100+ item), whether or not its to Canada you get appropriate tracking, or you risk losing the card, that is a fact of doing business on Ebay.
I also don't think its fair (to Canadians and yourself) to "cut them off" from making future purchases from yourself, do to this one negative experience (you said it was your first). From now on just make a cut off amount that you can't afford to lose (some US sellers do $25, some $50, some $100 etc.) and then advertise and charge the appropriate shipping charge to get it registered to Canada. Problem Solved. Just be upfront with the registered shipping charges and you will find that on items of decent value, most Canadian buyers won't have a problem paying the charges and if they do they won't bid as you have the price advertised up front.
Considering that the US/Canada are connected to each other and our relations are so close, i wish there was a way that our two postal systems could better work together and be more reasonable on the (registered) shipping prices especially.
Like someone else mentioned, Canada is a huge market for Sports Cards as well, 2nd only to the USA. We love our Baseball and Hockey cards just as much as you guys
