You'll need Garmin's street maps (City Navigator) in order to have the unit auto-route. While it can auto-route using topo maps, you'll find that the street data is out of date (by decades, in some cases).
It can't autoroute using Topo. It will try to autroute on the base map if you have Topo selected.
I've got the TOPO Canada map loaded onto my Legend HCX. It auto routes fine for me. I just mark a waypoint where I want to go, then click goto, then it asks whether I want to follow the road or go offroad (as the crow flies) and it figures out a route via the existing roads on the topo map.
The only reason I could see that I would need the City maps would be for the POI's. The topo maps give me outdoorsy type points of interest. Rivers, bays, points out in the water, parks, etc.
Perhaps it's different than your topo maps because they're Canadian ones. Not sure, but I know it works great as an auto GPS. I use it all the time finding places.
Willibauer