In my opinion, because you sell trading cards which can be sent by LetterPost/Light Packet, moving your stock to dotCOM may be a good move.
The reason has less to do with currency than with shipping.
On eBaydotCA, we have access to Calculated Shipping. For sellers of, say, hockey jerseys or teacups, this means they can give customers the exact cost of shipping no matter where the customer is, as long as they enter the correct (and metric) dimensions and weight.
But you don't need that (usually). So you could move to dotCOM, list in USD and use Flat Rate shipping from international location.
But take your time. You have 60 + days to decide.
You could start by moving all your relists to dotCOM, but we are promised a bulk relist tool come May, which with any luck will mean you don't have to scan all those cards again.
Remember that in Search, US customers see your prices in USD, whatever the currency the seller actually used. The listing itself will show both currencies. Does this panic your customers?
Note: if you often sell multiples or if you feel in some cases that you need tracking, you are allowed to upgrade the shipping as long as you don't try to make the buyer pay more. When you do it, it pays for itself by relieving your stress over a high value/high fraud transaction.
