In my opinion the only reasons to list on dotCA are that the item will mostly attract Canadian buyers (mostly memorabilia and history) or that the item must be shipped by parcel where the rates vary by destination.
If you are selling something small, light and inexpensive, list on dotCOM in US dollars.
In fact, I would throw in Free Shipping DON'T PANIC which simply means adding the cost of shipping into your asking price.
Which is cheaper?
A $1 card with $1.20 shipping or
A $2.20 card with Free Shipping?
In my opinion, the buyer would be less happy with the first, because the shipping is higher than the selling price.
It's all smoke and mirrors.
Also look at your records of currencies.
Are you selling mostly in Canadian? Are you selling mostly in USD?
Which is paying more?
That one threw me this month (too short a period for data, we're still in anecdote). While my US and Canadian dollar sales were about equal, the Canadian dollar sales were about a third higher than the US dollar ones. (I didn't look at destinations but I have seen an uptick in International sales since the switchover to loonies. Still anecdotal though.)
And those US sellers who are paranoid about tracking-- good! That means your Canadian and international customers are avoiding them too. You get a boost.
I also have an opinion (I get them wholesale from China) that buyers who pay more are easier to deal with than the 'armed bargain hunters' who bottom feed for lowest prices.
