I don't know for other manufacturers, but both my cars (05 Mazda and 07 Mitsu) are built 2 month before the delivery. I would expect fast moving cars, locally produced like Toyota and Honda, to be at least as recent.
I believe that Corolla is cheaper by few hundred bucks in Canada. No need to cross the border for it.
I believe I read an article few months back that there are only three cars - Corolla is one of them that are cheaper in Canada than in the US. I think the other two were domestics.
When I bought my Outlander back in March, I had a comparison spreadsheet for Outlander, RAV4 and CRV, US/CAD prices. The Outlander LS 4WD w/Convenience was (and still is) about 18% more expensive with the RAV4 and CRV being 30-36% more expensive in Canada. At aprox 1.16 exchange rate at the time, plus the 6.1% duties, it would've been more expensive to go south. Today you might be able to save few bucks buying in the US. Another thing to consider is that in the US, the purchase prices are closer to the invoice or below plus the freight is almost 1K less so some extra savings there too.
Kudos to Mitsu for not being greedy, although it's not like they can really afford to be.

Honda and Toyota can afford to sell at high prices in Canada, because people buy their cars regardless. The only way to make them lower the price is when people will stop buying their products, which I don't think it will happen.
The only thing that bothers me is that they deny the sale to the Canadian residents. I can understand the fact that these manufacturers would not honor the warranty in Canada, but they should if you bring the car to a US dealer. In this case, everything would be fine by me.