I agree.Unless I'm mistaken Canada doesn't require a passport (or Nexus Card) from US citizens. I've read that even today they'll take a US birth certificate and a driver's license.It's US Immigration that's the problem. I'll bet that if you arrive at US Immigration with a birth certificate and a license they'll let you in...but you might get some kind if fine.
At my first visit to Canada (1970) all I had to show was a driver's license.Same thing when returning.