^Good news.
Guideway Intrusion System @ YVR-Airport
About 2 metres behind the No Entry gates in the service corridors, there are these laser sensors that will be activate the warning message if one is beyond the platform edge. For stations that are 40 metres (I believe YVR-Airport is actually 50 metres btw), the sensor is actually located so that when the platform extension comes in, they don't have to move the sensors.

Photography by Deasine - Hosted on Picasa Web Albums - Creative Commons Protected
Thoes three black sensors at the end on the left.

Photography by Deasine - Hosted on Picasa Web Albums - Creative Commons Protected
Lasers are also located on the tracks, similar to the ones used on the Millennium Line.

Photography by Deasine - Hosted on Picasa Web Albums - Creative Commons Protected

Photography by Deasine - Hosted on Picasa Web Albums - Creative Commons Protected
I just noticed that if one falls onto the guideway, it's not going to be as easy to roll on the side underneath the platform on the Canada Line than compared to the SkyTrain as you'll have to roll over a concrete stub and a rail along with a few pipes. The Expo and Millennium Lines stns have level trackbeds at stations.