This is huge - and annoying. I like to avoid Amazon when I can, but if I can't figure out what shipping is going to cost until the cart is almost finished being checked out, I'll bounce.
With a lot of US-only retailers the only way to find out they won’t ship outside the US is to try and checkout and look for a country drop down.
And the ones that will ship, shipping for a small parcel can range from inconsequential (free/$10) through punishing ($80) to absurd ($300).
I don’t need an exact amount, but there can be a couple order of magnitude difference between stores when trying to ship to Canada and often no way to determine they even will at all without going through the checkout flow.