I am a Canadian living in USA. Do I need a passport to come back to Canada to visit or will the green card be sufficient? I will be driving. Also, will I need a passport to get back into the USA?(LD)
If you're driving, the green card should be sufficient. If you don't have your birth certificate or other evidence of Canadian citizenship, they can probably look you up in the computer or just take the green card as sufficient evidence (if it shows that you were born in Canada). US permanent residents do not require a visa to enter Canada, so it's not even certain that you'll need to prove your nationality.
To enter the US, the green card is definitely sufficient:
If seeking to enter the United States after temporary travel abroad, you will need to present a valid, unexpired “Green Card” (Form I-551, Permanent Resident Card). When arriving at a port of entry, a U.S. Customs and Border Protection Officer will review your permanent resident card and any other identity documents you present, such as a passport, foreign national I.D. card or U.S. Driver’s License, and determine if you can enter the United States. For information pertaining to entry into the United States, see U.S. Customs and Border Protection’s webpage.
As the phrase "any other identity documents you present" implies, such documents are optional, though since you'll be driving you should certainly have a driver's license with you.
For entering Canada by land, I believe that you can visit as a US permanent resident with a green card without needing a passport. The current websites do not give a very clear answer. For example, this webpage for Visitors to Canada says:
If you are a U.S. citizen or permanent resident, you must carry proof of citizenship such as a passport, birth certificate, a certificate of citizenship or naturalization, a U.S. Permanent Resident Card, or a Certificate of Indian Status along with photo identification. If you are a U.S. permanent resident, ensure you carry proof of your status such as a U.S. Permanent Resident Card.
The "or" seems to imply that one of those (e.g. a US permanent resident card) is sufficient. It doesn't say that a passport is required for US permanent residents.
US permanent residents do not need a visa to visit Canada. However, US permanent residents entering Canada by air would required an eTA, which would require a passport or other travel document (a US Re-entry Permit or US Refugee Travel Document). However, US permanent residents entering Canada by land do not require an eTA. The current Guide for Transporters (i.e. for people flying with an airline) mentions that US permanent residents need an eTA, which must be linked to their passport. However, an old version of the Guide for Transporters, from before the eTA requirement existed, explicitly says that US permanent residents traveling to Canada directly from the US do not need a passport (on page 14 on the page, page 16 in the PDF):
Permanent residents of the United States may travel to Canada from the United States or Saint-Pierre and Miquelon without passports, travel documents or visas provided they produce satisfactory evidence of their identity and status.
This strongly suggests that, were it not for the eTA requirement (which doesn't apply to entry by land), US permanent residents entering Canada directly from the US do not need a passport.
For entering the US, as far as the US government is concerned, a returning US permanent resident with a valid green card does not need a passport. This CBP FAQ says:
United States (U.S.) LPRs do not need a passport to enter the U.S. as per 8 CFR 211.1(a)
And the Carrier Information Guide, page 28, says:
A Lawful Permanent Resident may travel to the United States without a passport with a Permanent Resident Card (Form I-551).
This page has a list of documents that "can denote identity and/or citizenship". There's also a list of documents acceptable for establishing citizenship and identity.
The US green card is not in any of those lists.
You should understand that a green card is a document issued by the United States and, subsequently, does not establish that you are actually Canadian.
You should examine the list and, if either time constraints or the outrage of the requirement to pay no less than $160 for a 10 year passport precludes the possibility of getting a passport, use those documents. They might also be helpful in allowing you back into the United States.
If you were flying, you would almost certainly need to use a passport.