Salut Gunnar!
I have the same problem, and never did satisfactorily find a good online store with great shipping. I didn't mine NewKadia.com. They aren't in Canada, but you can get Canadian prices, and I think I remember the shipping being reasonable (but I might be misremembering).
There's also Comics Detective, but I don't know their shipping rates.
http://www.comicdetective.com/index.html
As an alternative, perhaps make a point to visit bigger comic book shops whenever you visit larger cities? I'm closer to Ottawa, and the store I go to is good for preordering, but bad for just browsing for older material (and the other Ottawa stores are too expensive). So whenever I'm in Toronto, I make a point to visit the various stores that are on Yonge Street (as well as a large BMV retailer on Bloor Street) that have good selections and decent prices.
And then, be sure to go to Conventions. The Ottawa one is in a week, and all the retailers in the region set up booths with great selection, and some are pretty cheap.
So, in conclusion, the internet hasn't been great for issue collecting in Canada, but the retail market is still pretty good.
Bonne chance à trouver ce que vous cherchez