Depends on the border agent as well. When I came across the border with my wife, we had the application ~50% complete and I had a Uhaul full of stuff. I told the female agent that I was planning on filling out the application and waiting as a visitor. She gave me a hard time about bringing my stuff but she was very nice and ended up giving me a 1 year visitor record. On another trip to the border, the agent I spoke to was shocked that I had been let in with so much stuff, but it was fine. I always told the truth to the agents, and they usually respond to that. Once you start dancing around the question of your intentions, everything spirals down from there
I think it's strange that they give you 6 month or 1 year visitor records and still expect you to show ties to the US. How can you realistiically do that. The only evidence I brought was the immigration package and a copy of my bank statements. If I am planning on travelling for 6 months, I won't have an apartment to lease, a job to go back to, or anything really besides friends/family. What have other people used as ties? Because when it comes down to it, your real ties are to your spouse, and you are residing in Canada as a 'visitor' but never intending to leave. Sometimes I wish CBC would just drop the charade and say it's OK to come and do that from Visa-exempt countries. Would make things a lot simpler and less stressful.
About the car....it is not legal for Canadians to drive US plated vehicles. That being said, I doubt a cop would give your husband a ticket if he pleaded ignorance. If he got into an accident, that might be a different story for insurance and everything. I am driving my US plated vehicle up here while I wait for PR. My auto insurance company has been calling me, and I have told them that I am travelling and using my parents mailing address. The money keeps coming out of my account, so I still have coverage.
I tried to import my truck so I could switch to Ontario insurance, but the agents at the POE wouldn't let me. I don't know if they were correct, but they said that I couldn't import it as a visitor. Before that, I had gone to Service Ontario to ask about it, and they said that I had to go to a POE (I went to Hamilton airport) to get a form or something. So I went, and they told me to just wait until I get my PR to import it. It's almost impossible to get a speeding ticket here in southern Ontario, so I don't anticipate any problems with getting pulled over.
Anyways, let us know if you find any info out about the car stuff