You should look into AC's stopover program.
http://www.aircanada.com/en/travelin...ver/index.html
If you bought your ticket on AC.com you might be able to purchase lounge access as an a la carte option. This access is supposed to include connections, so I would think this would work (although I don't know for sure).
The link I've provided mentions purchasing lounge access for connections of 6 hours or less.