Most of the retailers web forms can't handle Canadian purchasers but a quick phone call normally settles everything and both sides are happy.
I just ordered a bunch of wine from Crush in NYC. You'd think that they are a big-enough retailer to have a decent web site.
Indeed, they do recognise that there are other countries in the world. And when you pull down the list of 'states' for Canada, it does show you the appropriate selection of provinces. But then they demand that you give them an all-numeric zip code which I couldn't do. So we had an impasse. I phoned them and the person I spoke to said that they get all kinds of complaints about their web site. So why don't they just fix it?