Can I enter Canada by car (my own vehicle) with a 2-month expired passport? Also, am I able to re-enter the US with the same expired passport. I am a US citizen.
No, you should not be allowed into Canada with only an expired Passport as it is not a valid ID.
If you enter Canada using Proof of Citizenship, you should expect trouble returning to the US with only an expired Passport as the Canadian and US border requirements are different, even for US Citizens.
It might be slightly easier than if you had no ID at all but as you don't meet the entry requirements, CBP can process your entry at whatever pace and using whatever methods they see fit.
You can re-enter the US from Canada by land using any of these documents:
- U.S. Passport; Passport Card; Enhanced Driver’s License; Trusted Traveler Program card (NEXUS, SENTRI or FAST); U.S. Military identification card when traveling on official orders; U.S. Merchant Mariner document when traveling in conjunction with official maritime business; or Form I-872 American Indian Card, or (when available) Enhanced Tribal Card.
Can you? ... maybe. It's up to the discretion of the border officer whom you receive in the luck of the draw. If convinced that the document fairly identifies you, the officer has the discretion to accept it. In practice, there is a strong chance that you will be refused admission.
As for returning to the U.S., as a citizen you have a right of entry, but the border officer has to be satisfied of this fact, so there is an elevated chance of delay while the validity of the information in your passport is sorted out. (Remember that expired passports have an elevated chance of lacking modern technology, so are more easily forged.)
If you lack one of the alternate acceptable methods (trusted traveler card, enhanced driver's license, passport card, etc.), then it would be a very wise idea to renew your passport, unless you live close enough to the border that you can afford to take the risk of being refused, and don't mind the extra delays that this could cause.