yes u need it for sure

I went to Clerk of the County Court for an application. Biggest hassle was going to get a 2" x 2" picture taken to fit on the passport. It came in the mail within two weeks if I remember. Not a lot of trouble for going out of country. Better than going thru a hassle when you have someplace to get to.
Kinda like being difficult with a cop when you get pulled over for a taillight being burned out.
I did learn that the personnel at the Cancun airport don't have a sense of humor when going thru customs. None at all.

I also know a couple that got in hot water when they took boot jacks with alligator skin into Canada. Alligator is illegal in Canada apparently.
Also they got in trouble for not paying sales tax on items when they crossed the border, just in case they did sell them while in Canada.
Also have heard of people having to pay sales tax on tobacco and alcohol at the border.
Welcome to Canada! Enjoy your stay!

Short answer is NO, you don't "need" a passport to cross into or return from Canada if you are a US or Canadian citizen and can otherwise prove it.

I cross back and forth several times a year delivering our setters etc. and use the passport card. I just keep it behind my drivers license. Last year I mistakenly gave them my DL instead of passport card. The guard said "oh, no passport eh'". I apologized, and gave him the passport card. He said it was usually faster with passport but not required.

Since then I have talked to several people who have crossed back and forth without passports, for a variety of reasons. If you read the "required documentation" section of both Canada and US you will see it always says something like "to avoid possible delays while citizenship is confirmed" or "it is recommended you have...", when they discuss passports.

I like to take sunglasses and hat off while approaching the booth, if guard see's you do it all the better. Turn car off and keep hands on the wheel in plane sight.