Actually, I believe that most breeders are selling to the US. This is especially true for high-end morphs, as there is stronger demand there, and better prices.
For more modestly priced animals, the Canadian market is fairly robust. If people are still going to the US for these animals, then I think that it boils down to a lack of information and ease of use. For example, very few Canadian breeders maintain a regularly updated website with individual pictures of available offspring. I feel that this is essential, as one of the first questions you are going to ask the breeder for is a list of all available offspring so that you can take your pick. Sending emails back and forth about which herp you want is a tedious process. Most breeder sites just have a gallery, and a basic price list. There is no 1 click shopping, you usually have to email or leave a message on an answering machine to initiate contact, which may take a while.
Personally, I prefer to buy from Canadian breeders, since it cuts down on the paperwork as well as shipping costs. Also, the quality, variety and availability of different species have grown by leaps and bounds. We are still lagging behind the US, but the gap is closing.
Just my 2 cents.