List in US dollars.
All the world knows USD and Americans know no other.
Set shipping costs for USA.
At the moment, your listings say
"Shipping cannot be calculated"
Why on earth are you charging $16 for shipping (ECONOMY?) a $28 comic book within Canada?
While you may want to use a tracked system, you should include at least part of the cost in the asking price and use Free Shipping if at all possible.
Which costs more?
A $10 item with $15 shipping?
A $15 item with $10 shipping?
A $25 item with Free Shipping?
Which gets the most bids? Which buyers are happiest with their purchase?
Comics are pretty easy to ship with Flat Rate Shipping.
I sell on dotCA and have no problem attracting US buyers. The rep is (as usual ) wrong.
BTW-- good title- Mentioning Rocket Raccoon during the premiere week of GoTG was a smart move.