This is a concern right around the world. Certainly, off the top of my head, there are not other nations who, when proceeding under immigration proceedings, use the high standard of beyond a reasonable doubt necessary in criminal proceedings.
I think the reason so many organizations are saying that criminal law is really what needs to be pursued here is a combination of the fact that this isn't just any old immigration proceeding.... Number one, there are almost always very serious human rights concerns at stake, such as torture, arbitrary arrest and detention, who knows, but there are serious abuses waiting at the other end of the deportation. There is also the fact that serious allegations are being made about security concerns. Immigration remedies don't get to those either, as they just brush them off our doorstep and make them somebody else's problem, perhaps increasing the possibility the person will be able to continue with plans, and maybe even eventually mount an attack of some kind that will bounce back towards Canada.
So we need to be looking very seriously at the criminal law system, because that's the best way to deal with it.