I'm not sure if this quite answers your questions but here's a snippet from their FAQ section regarding payments:
"International Payments
We accept orders from most anywhere in the world. All payments must be made in United States Dollars.
Your credit card company converts your currency to USD at the time of purchase using the current currency exchange rate. We do not control the exchange rate, nor any foreign transaction fees your issuing bank may charge."
https://www.bigbadtoystore.com/Help/Payments
You could always just fire them off an email with your inquiry. I'm sure they'd be able to clarify for you
However, I have used them in the past before and every time I got hit with customs fees. Obviously, the size of the order will determine how much you actually have to pay.
For me this was a deal breaker as the currency conversion, shipping costs, and customs fees generally outweighed any deal I felt I was getting. Since then I've waited until products are sighted in Canada, and/or purchase from one of the sponsored retailers on the right-hand side of the page here.
But in your case, with a gift card, purchasing from them is your only option
Best of luck with it, hope you get something you enjoy out of it!