Stranger,
Legally you are not required to present a valid US passport to cross the US Canadian border at this time, but that might change next year. Whether you would have any hassle depends on a number of factors: whether you look like a US citizen, talk like a US citizen, behave like a US citizen, act in any way which may raise suspicions, your demeanor, and not the least is what mood the US or Canadian officier is in.
For most people a valid US driver's license is sufficient. I know many people who have done that without any problem, at least not on the issue of citizenship. The expired passport is a good supporting evidence of citizenship, but if I were you I would definitely carry another form of valid picture ID to prove who I am.
Even if you were a naturalized US citizen say from South America or Asia, I would think a valid official picture ID such as a driver's license and an expired US passport would be more than sufficient to get you thru the US Canadian border, at least for now. But don't be too surprised if you were asked a few more questions and got invited to a longer getting-to-know-you-better chat inside the building.