Up in YYC/Calgary the local preboard security stations at the new international terminal are operating under the same specifications as what UA is installing.

Here is a CATSA video to explain how the whole system works. The video from 1:50 point explains the xray system and automated bins.

As to the question about why everything needs to into the bins, check out 2:48 point to see how the bin diversion system works. Bins that require additional screening are removed from the normal flow. To enhance efficiency of the lane and provide continuous movement of bins, the xray technician screeners are located in a seperate room. There are more screeners than active lanes. If the remote screener requires a specific bin to undergo additional screening, the xray belt diverts that bin over to the additional screening lane. If everything was not located in a bin, the contents could not be automatically diverted without destruction of the belongings.

If you have a hard time and are choking on the government spokeshole propaganda , the CATSA video is available in french here:
The french version has an additional 10 seconds onto the front of the video compared to the english version.