There may actually be a good reason for the Canadian Rogue spoiler design:
Transport Canada has a standard (Techincal Standards Document #108) that requires stop lamps be visible +/- 15 deg from the horizontal (up/down) and +/- 45 deg from the vertical (left/right). This would also include the center-high-mount-stop-lamp (3rd brake light)
http://www.tc.gc.ca/roadsafety...%2019
It's possible the US spoiler didn't comply with Transport Canada Regulations and was covering up the center mount stop lamp, so perhaps Nissan had to redesign it. Actually, from the photos I've seen of the US spoiler, I am almost convinced... it seems you can barely see the 3rd stop lamp.