I did something pretty similar recently. I bought a californian Bike in Argentina from a guy from New Zealand (I am german).
The vendor flew to LA for some days before heading back to NZ, so he took the papers with him to transfer the Bike on my Name. As far as I know that was no problem, all he needed was a copy of my passport.
Before leaving he wrote me a Document that said that he gifted me the motorcycle because he had to fly home for urgent family reasons. We didn't get a notary stamp or anything for that, just signed it both.
Because i had to get to Chile and couldn't wait for the papers to be sent to Argentina we also scanned in the papers, changed the name, and printed them out on some regular ink-printer (didn't even laminate it or printed both sides).
Because many many people in Argentina told me that I won't get across the border with this because the importation documents still are in the vendors name and the writing that said that he gave it to me had no notary stamp or anything that proves it as genuine i looked for a smaller border to cross over to Chile.
I crossed at, i think it was called Paso Vergara, a bit south of San Rafael. Beautiful landscape on the way an absolutely no problems at the Border. It took me about 10 minutes to get across the argentinian Border and into Chile.
I would not recommend to do it as I did. It is definately better to get a notary Stamp or to take the ferry to Uruguay together with the Vendor. But there are definately possibilities to buy a foreign motorcycle in Argentina.
I also read some threads here in the HUBB before buying the bike, and there are people who always say that there's absolutely no way to do it. That just simply isn't true! There is always a way, and in that case it isn't even that hard.
Oh yeah and you can also get an insurance in argentina for all of south ameria if you have problems with that in canada. It's super easy, just go to ATM in Buenos Aires (I think it's Av. Florida 833 (not sure about the number)) They will give you an Insurance for 60 Pesos per month (may have changed) in 10 minutes (for the extension for all of South America you'll have to wait 2 or 3 days).
I can only tell you what I experienced, but in my case it worked fine like this.
Good Luck with your stuff!