Haha... Valid point. I'd have to explore the intricacies of Canadian songwriting before I could confidently make the assertion, but my feeling is that Cohen's songwriting falls in line with the American tradition.
I'd say Cohen is entirely Canadian. He has this very self-deprecating humor that you don't really get from Americans.
Leonard's first album had amazing production by american producer John Simon (who also worked with The Band, Simon & Garfunkel, Janis Joplin), probably the best in Cohen's entire career, so he chose well deciding to work out of Columbia's studio in NYC...
Not sure what else you can call someone from USA, so I guess it makes a bit of sense.