Having done all 3 of those, I'd say that Canada was my favorite of the 3 and one of my absolute favorite all-time IMs (of the 17 courses I've completed). Boulder is near the bottom of my list. Wisconsin is near the top of the list but Canada was probably my favorite in North America because of the scenery. Canada is a tough bike course with lots of climbing and I'm not a strong cyclist or climber but I loved the day.