The big problem is that you mix up two completely different situations regarding the security risk. The refugees flowing into Europe right now have a much higher security risk, because it's fairly fast and relatively easy for terrorists to use that cover to buy their way to Greece and once in Europe use contacts to reach Belgium or France etc. The trip takes days to weeks. This is quite realistic, and frightening. This is what most likely happened in France with at least one terrorist, that is if ISIS has not developed other means to send secretly EU nationals back into their home country using secret contacts in Turkey etc., like the leader of the cell involved in Paris (a French national) might have done. There's not UN screening done, no investigations. Tons have fake passports, and many countries are lacking resources to properly catch those.

That's one thing.

The other thing that hasn't changed one bit with Paris is the situation of the camps in the middle-east countries (Jordan, Lebanon etc.) where refugees are already duly screened with background checks by the UN. The majority of those are women and children, the majority of men are either the fathers, old men or boys. Many of them are orphans. A great deal of those refugees have been there for 3, 4 years now, so before the true rise of ISIS. A lot of them are middle-class, well educated people, perfectly apt to integrate well in western nations. They're screened by vulnerability and needs, and also for their desire to resettle abroad permanently given the chance. It's those people countries like the US and Canada are asked by the UN to take care of, to unburden the region but also to make room for new people in the UN camps, and to attempt to slow down a bit the flow into Europe at the same time. There's no question at the moment of the US or Canada choosing refugees from the pool of people already in Europe.

The risk level with those people is already low, and to be lowered still once the US and Canada's secret services will have further investigated the ones that get picked.

It's pretty ludicrous to believe that 3-4 years ago ISIS or even AQ could send to those camp moles without even knowing if, when or where they'd be eventually sent, all the more since single young men need be in dire need to make the priority lists. There are much, much easier and much faster ways to infiltrate commandos into Europe or even the US, or to radicalize westerners (which so far represents the biggest risk, by far).

The people in the camps bring no more security risk than the other muslim refugees that have been welcomed in great numbers in North America over the years.

Those governors are being politicians thinking of their next reelection by appealing to the irrational fears of their electoral base, at the expense of people in dire need of help.

Anyway... the new Canadian government has implemented its plan to welcome 25,000 Syrians over 3 months, starting Dec. 1st. In four years they'll be citizens with passports, perfectly able to enter the US with ease. So unless one of the clowns gets elected and build a wall between our borders before then.....