I've been doing eBay since 1999. I learned a lot about shipping through trial and error.

Canada Post is pretty good about the time and delivery of your items. I usually got my stuff around 2 weeks from when I paid the items, no matter where the seller from (as long as the seller ship right away). The bulkier or heavier the package, the more likely the customs will open your package. But most of the time, if you could provide all the required information, you could always get a refund on the customs fees through Canada Post.

Beware of seller that ship through UPS though. UPS really sucks! It might look cheap when you paid the shipping through the seller, but at your end, UPS won't release your item until you pay all kinds of extra fees. They add customs, brokerage, delivery fees, etc...even though there is no customs on the item through regular post mail. I guess UPS ships all of the packages through big box all at once, so they incure all kinds of fees and they just add them to the receiver of the package. These fees are NOT refundable!

With FedEx, it depends on the services the seller use. I once got a huge box full of stuff, about 30" x 35" and weigh about 30 lbs, but didn't have to pay any extra fees. Just sign the form and got the package, hassle free. But once I got a smaller package, about 12" x 12" weight about 1 lbs, but had to paid extra brokerage fees, etc. So, you have to make it clear what kind of service the seller uses to ship your package with FedEx.

So, I hope this long explanation helps!