Almost all major manufacturers of laser printer cartridges provide a mechanism for returning spent cartridges (from what I can tell free by courier) as long as you are in the United States (and seemingly in Europe as well if the literature in the box is any indication). I am guessing this is not voluntary (or at least not without some government coercion).
None that I can find offer the same service for Canada. Why is this? Are Canadian governments lax or behind the times with recycling laws in this area?