For me it's Adobe. Stupid government and other forms I need for work. No available third party software will work on some of them, and I've tried them all. And for some dumb reason even having an Acrobat subscription won't let me fill them out on their (extremely buggy, by the way) web app.
Was never able to get it working with wine.
That, and the compatibility between Libreoffice (or other Linux office software) and MS Word is still terrible. I'm quite sure that's mostly due to shenanigans by MS. So if you have to swap documents back and forth between people (e.g. with track changes) it just doesn't work as well. And, like Adobe, the web app version of Word seems to be kneecapped in a few key places.
I don't think it's possible. Rock Auto doesn't list the country of manufacture. I'm pretty sure it's because very often the exact same item (part, brand, and serial number) is made in different factories in different countries. I've ordered the exact same thing and sometimes it says made in China, other times Mexico for example. I'm pretty sure this is true regardless of which retailer you order from, so unless you are physically looking at the item before you buy it, you probably won't be able to know. And these days, even going to my local parts store, they will most of the time need to order parts in from elsewhere.
If you're asking if there's a Canadian alternative to Rockauto, I'd also love to know.