‘Canadian exceptionalism’, roughly, refers to the absence of any significant anti-immigrant or anti-diversity sentiment—and the consequent absence of a nativist or right-wing populist political movement—in Canada.
The post has the virtue of identifying institutional, geographic, and policy factors that help explain this exceptionalism, rather than appealing to some kind of amorphous 'spirit of toleration' that makes us Canucks so welcoming. More specifically, Heath identifies the following factors as relevant: (a) the existence of very little illegal immigration to Canada; (b) the policy of bringing people in from all over the world; (c) a political system that encourages moderation; (d) the policy of including immigrants within the larger nation-building project; and (e) the institutional protection of the majority cultures (French and English) throughout the process.
Happy (belated) Canada Day!