Also in Ottawa, on the 18/0.5 package:
So while my download is showing a little slow (though worth noting my Steam download I just started is jumping between 15 and 18 Mbps), I'm not seeing numbers as bad as yours. And I never
see my upload speeds drop. It could be local node congestion, or it could be something on your end - wiring, modem, etc.
Edit: I'm also on a D2 modem, which is what I've been blaming for the small drop in peak-time download speeds.