If you haven't already already read littlebrudders diary on this topic, please check that out first.
To begin with, let me say this. My first political job was as a canvasser. I did it for three years, and about two years later, I founded a canvass-based local political organization that completely transformed the local politics of the area where I live. We ended up with some of the most progressive environmental and land use policies in the nation, and elected majorities on most of our city councils when I left my position as executive director after 10 years.
So I have canvassed, I have run canvasses, and I have managed canvassers, field managers and the whole ground game of clipboard-and-shoe-leather organizing. And I've been doing nonprofit fundraising in modes other than canvassing (grants, major donor, direct mail, events, etc.) for a long time now, too, so I see canvassing in the context of effort required vis a vis funds raised.
More on the flip