I'm curious: what reputation does the Canadian postal service have? Speaking of one who uses it quite regularly, I would say that cross-country parcel service can sometimes be quite slow (though no worse than what I've experienced with domestic USPS standard parcel), but letter mail is usually pretty fast, and very reliable. Mail within the same urban centre is often delivered next-day.
The 8th was last Monday. Depending on time of day, something dropped in a post box on Monday might or might not have actually made it out on Monday. Yesterday was a holiday in the US, yes? So you're talking 4 business days, at best. Even within the US, I'd guess that you would be very, very optimistic to assume that documents sent by regular mail would be both received and processed by the closing company in that time frame.
Again, the extra couple of days that
might be attributable to your international seller just isn't significant on the overall process here. If you'd chosen a seller in the US, you might have gotten someone who sat on the documents for a month. Or who had to get their ex-wife, who now lives across the country, to also sign the documents. Or maybe Disney might have taken an extra couple of days on ROFR, or the title company got busy and your contract is just not at the top of the pile. It's the just nature of the resale process.
I understand your impatience, truly. But as many on these boards have pointed out, the worst wait (for your membership number) is still to come. And can take weeks. My guess is that your contract will close a few days ahead of your 2/29 "close by" date, and it will have nothing to do with where your seller is located. That just seems to be the experience most people are having with the big closing companies. I hope that you are lucky and it closes sooner! In the meantime, sit back and remember to breathe.