Most of my items ship LetterPost/LightPacket, so I have moved them to dotCOM and use Flat Rate or Free Shipping.
The few that are bulkier need Calculated Rate parcel post and have remained on dotCA.
That being said, I have not seen any great difference in the number of sales, and those listed in Canadian dollars have been purchased from customers from the US and UK although most are postage lots sold to Canadians (and not really of interest to non-Canadians).
All the other overseas customers bought USD items.
BTW and off topic-- what is your reasoning behind penny shipping?