PTO (Personal Ticket Office) is AC's own booking engine. You can download it from http://www.aircanada.ca/pto/home.html. You will get a popup saying that you must have been contacted, but you can ignore that. Once you have installed the program you need to call the PTO tech line to activate the service. I was able to do that as an Elite a year or so ago, but I don't know what the status requirement is.

On the blocked seat question, I think that Empress means that on the PTO seat maps you will see that the seat adjacent to the one you have requested will also show as filled.