Actually, El Salvador is the only Central American country that I have visited that actually inserts a large visa sticker into the passport upon arrival and then stamps that. It easily takes 3/4 of a passport page or possibly a whole page depending on how it is positioned. It is then stamped on arrival but not exit upon payment of USD 10. Not sure if this is required from Canadian citizens, but I imagine it likely is. The previous poster may not have encountered if he holds a passport from another Central American country.
Years ago, I recall that Panama stamped on both entry and exit, with a round quarter-page stamp. On my most recent visit, they only stamped on entry.
I don't recall the airline ever checking that I had sufficient pages on trips to Central America as they do in the case of South Africa. You never know, but I probably wouldn't be too concerned.