Canon. I have had experiences with a friend who had a bad lens he bought over seas, which even where he bought it from was a grey market import from Korea. Sent to Canon they sent it back fixed within 3 weeks.
As far as I know Nikon are the only people pedantic about the grey imports, and even then it depends on the country. Nikon Australia is more than happy to honour warranties on international products (I know because I had an issue with a flash bought in Austria and called them but in the end I didn't need to send it in). They just don't honour warranties on serial numbers either not in their database or of known grey market products.