" the US Buyer will never rate my shipping costs reasonably"
Let's be honest. Buyers anywhere in the world, including the USA, do not care what your shipping costs are. It is none of their business.
On eBay, you compete globally. Whether you ship from Canada, Australia, the United Kingdom or Germany, the buyer only concern is "how much does it cost me"?
And they rate sellers accordingly. If they can purchase an item from seller A with a $5 shipping charge and a similar item at a comparable price from seller B with a $10 shipping charge, odds are seller B will receive lower DSRs than seller A.
It has nothing to do with fairness. It is business.
At the end of the day, all Canadian sellers selling outside the country, need to ask themselves :
Can I compete in the American (or overseas) market on a "landed cost" basis (including shipping)?