Don't count on the topo maps being consistently reliable across the map, even though you know it depicts every little bay and rock shoal on your canoe route. I first found this out when trying to explore the land beyond the shores of the French River. On a recent trip into the Kawartha Park, we used a topo to try to reach a lake by bushwhacking, and were thoroughly thwarted by the terrain and the inadequate representation that the topo map gave.
Here's the topo map of the area. We tried to cross from Buzzard Lake at the left edge of the map to Elm Lake at the bottom. The topo 1:50,000 has a lot of the details, like wet expanses with open water just represented as "green" = forest.
Google will reveal that there is a lot more water in reality, but the resolution is not good enough to make an accurate judgement of what's ahead.
If you should have a GPS with built-in map with you, like the Garmin topomap, it would tell you just fine where in relationship to the large lakes and the elevation lines you are, but there is no hint of the wet obstructions that are ahead of you as you are trying to cross the land.
Ontario has a crownland-use-Atlas which shows the best details. Note all these little bodies of water that are in the area - and you still don't know whether you can cross or have to do major detours...
Here's a picture of what it looks like, standing on the ground and trying to figure out where to turn:
So, here's the moral of the story: Do not trust the detail of your topo when away from the commonly trodden areas!