A standard 1-oz letter to Canada (or anywhere in the world) is just US $1.20. However, package rates are much higher, often double or more the per-ounce letter rate. $13.54 does seem a bit high, but it's not necessarily *that* outrageous if the seller is compensating for
ebay and PayPal fees. At 13.54, the seller would be left with around $11.75 after fees, and, depending on the weight and what kind of mailer it's in, the postage itself could be up to $9 or so. If the mailer costs another $1, there's not all that much markup there. That's a lot of assumptions I just made and the seller may well end up shipping it at the letter rate and pocketing $10, but if those assumptions are correct, the shipping isn't necessarily terribly out of line.
Some sellers also don't really like to ship internationally, mostly because they're worried about lost/stolen shipments. Rather than just not shipping international at all, they just jack up their rates sky high to ward off buyers and/or make it "worth their while" to ship there.