I think they can see quite a bit. My understanding is that they don't keep the images of the screening or the body scanners. If you look at their screens as your bags go through, that is perhaps how they look at it. You can then be subject to a secondary search if they see something suspicious. You will remember that when you enter and leave Canada, there's a declaration, “Are you carrying more than $10,000?”
On April 26th, 2012. See this statement in context.