I find that the CN maps shows much less detail although sometimes OSM is missing entire lakes that show up on CN.
I think it's good to have both loaded and use the one with the info you need.
Here's a screenshot of the CN map from the same area you posted.
I don't have the topo maps but from what I've seen they are impossible to read.
Still hoping to find "terrain" maps like google and mapquest OSM so you can see some contour without all the lines.