Welcome, Tammy! Has he definitely outgrown the AOE? At his height, he will likely outgrow the carseat by height. I am assuming you have the harness straps in their top usable harness slot position. Please see this very helpful post:
http://www.car-seat.org/showthread.php?t=39120
If his shoulders become level with the harness straps, then you need to make sure they do not go above the harness straps. If they do, then the seat is outgrown. If they are below the harness straps, then you have a bit of time.
The reason that I mention this is because there are two new carseats that should be making an appearance in Canada in the next few months. Right now the Radian and Marathon are great picks if you need a seat right now. I would really recommend the Radian over the Marathon because it is going to last a bit longer (a year or more) than the Marathon. The top harness slots on the Radian are an inch higher than the Marathon. I do agree with PPs that both are great seats. What type of car will you be installing the seat in?
The new seats are the Graco Nautilus and the Britax Frontier. According to speculation, both of these seats would be great for you. The Britax Frontier is expected to ship to Canada in June, and should be here shortly after since they ship from the US. We don't know when the Nautilus is expected. The advantage of these seats is that they would last even longer than the Radian (harness height-wise), and they do convert to a booster. HTH and doesn't confuse you even more....
Let us know what type of vehicle, because the Radian installs great in some vehicles and is difficult to install in others...