Canada is decidedly not a 2 party system. There are 5 parties in parliment in total, although the Greens only have 3 seats. Yes, 2 parties tend to hold power, but we also end up with the ruling party only having a minority (as is currently the case) from time to time which makes for a very different dynamic. The biggest difference between Canada and the US is that Canadian voters can and will act to kick a government out of office when they aren't acting in the interests of the people, sometimes shifting the makeup of the government significantly after a general election. Ridings also aren't gerrymandered insanely, so there are many seats which can shift parties.