Until now, Canada is not a country that has openly committed military forces to conflicts where the adversary uses terror attacks on our soil as a weapon. Yes, there have been the occassional half-arsed terror plots in the past decade or so, but unlike some European countries and the US, we've not had commuter trains, subways, airports, and buildings bombed by radicals.
The number of European and North American passport holders fighting with Islamic State (IS) means the organisation is capable of attacking countries in these regions through terror. By way of comparison, the Taleban are a regional tribal entity, not an international terror organisation or Caliphate-bound army, and therefore posed little actual threat to Canadians on our home turf. They merely hosted a terror group and were punished severely for it.
The undemocratic decision by the Harper government to commit Canadian military units and arms to fighting IS increases the likelihood that sympathisers and returning combatants will launch attacks in Canada and kill Canadian civilians. This is an enemy that can hit back.
We shouldn't be surprised. It's not like Canadian lives ever matter to these fuckers anyway.