I'll give a real world example from when I was looking for a TWD Premium. Without naming names and using current exchange rates, and keeping in mind that the USD price was before Stern's minimum sale price thing went into effect:
Canadian - 7195 USD (no shipping). ~9050CDN at current posted exchange rates. Now I know that no one gets those rates, but they work for sake of argument.
US - 6300 USD (no shipping) ~7930CDN. Let's say that the Canadian distributor is converting exactly at the posted rates, but buying from the US you are using a standard credit card, and we'll add 3.5% to the conversion just to make things "fair" and call it $8150.50 CDN instead. I have a no foreign currency fee card, so it wouldn't be this high.
Now we add the GST (Being in Alberta we only pay the 5%). Brings our new totals to:
Canadian - $9502.00 CDN.
US - $8557.50 CDN.
Let's add shipping.
Canadian - I seem to remember from previous purchases that it costs about $300.00 CDN to get a pin shipped to the door from a distrib (not sure about GST on shipping or not, so let's say GST is included because we are kind). So our new total is $9802.00CDN.
USD - Let's forget any savings you might make by going down to the border to pick it up. I know from buying pins out of the States that it will cost about $500.00CDN LTL to my door. If getting it shipped you also have to pay a customs broker. Again, I know from experience that this will cost $75.00. So our new total would be $9132.50.
So all said and done, dollar to dollar, expense to expense, even being "unfair" to the US purchasing side, there is a $670.00 savings buying a Premium out of the States vs buying it "locally".
I wouldn't mind paying a bit more to support a Canadian distributor, avoid brokerage, etc. So in this scenario, if I could get the Premium from the Canadian distributor for $6800.00 USD, (still several hundred USD higher than the US distrib), it would bring me to $9288.00 which is about $150.00 more.
It is entirely possible that I am just getting crap quotes from Canadian distribs, and other people are getting way better deals, but I can only go with the numbers that I have been told. And with those numbers, buying from a Canadian distributor just makes no financial sense.
Where I am really unclear on is how Canadian distribs handled Stern's new minimum sale price policy. That has added about $200.00 USD to the purchase price of Premiums for the average US distrib. If Canadian distributor prices have remained the same, then things aren't that far apart. If they decided to bump their prices even further, the bending over continues.