Yes, the peaceful Belgians. Why would anyone want to attack them? Only the attackers know the specific reasons, but I would offer that it's probably due to some combination of the following:
1. Brussels serves as the headquarters of both the EU and NATO, two "Western" organizations that jihadists despise.
2. Belgium has a large, mostly unassimilated population of Muslims. Unlike in the US (another reason why we're not quite as susceptible to these kind of attacks as they are in Europe), European Muslims aren't as efficiently assimilated. They're largely ghetto-sized in Europe, but specifically in Belgium. The results are self-evident.
3. Belgium has long been a relative safe haven for jihadists, largely due to the fact that the Belgians, like most Western Europeans, didn't want to be perceived as "anti-Islamic" or "Islamophobic." Since it was a veritable safe haven, attacks against Brussels were largely off-limits, as the jihadists didn't want to mess up a good thing going, Brussels acting as it was as a nice place from which to plan attacks elsewhere or from which to recruit and coordinate men headed to fight the good jihad fight in Syria. Once Brussels decided to crack down for once, the results have, again, been self-evident. It's no longer a "protected place," so the jihadists will no longer exclude it from their list of targets.
On a related note, I have read much intelligence literature that suggests that Canada is very similar to Belgium, in that, in an attempt to avoid "Islamophobia" over the past couple of decades, the Canadian government has turned Canada into a veritable jihadist safe haven. Several plots against the US have been hatched there, perhaps the most notable being the proposed LAX attack some years back that just happened to be stopped by the whim of a meticulous US border agent. If you'll notice, there are never any actually coordinated, planned attacks against Canada or Canadian assets/targets. The one attack was by a local with serious mental illness, who just decided he was going to go "jihadi" one day and attack Parliament. It was not a coordinated or sanctioned attack.
If Belgium is any indication, you can suspect there to be a sudden batch of attacks, seemingly out of nowhere, against Canadian targets, should the Canadian government ever decide to stop playing footsy with jihadis on Canadian soil. Ahmad will then be more concerned about striking back at the evil Canuck bastard that just imprisoned his good friend, Muhammad, than he will at the evil American Satanists south of the border.