And of course, for those items that will ship Letter rate, why not go to Free Shipping?
You get benefits in your DSRs. You may see more sales. You get a break on all Shipping FVFs not only the domestic ones when you off Free Domestic Shipping.
I would suggest using Free Shipping for Canada and putting your US shippng fee at $0.00.
Remember that Free Shipping is a selling ploy. You actually should be adding the cost of shipping into your asking price.
Which is cheapest:
$5 item with $1 shipping
$1 item with $5 shipping
$6 item with Free Shipping?