In '09, after getting laid off I did a road trip around with provisions for "I could go camping if my road trip took me that way." No fire arms or criminal record.. but I'm getting to that.
So, going from Seattle up to Banff by way of the Sumas / Huntington crossing...
I went in and was asked for the purpose of my visit ("tourist"), duration of stay ("one to two weeks, no more than two"), for my occupation ("I am currently unemployed") and my permanent residence ("I am currently without a permanent residence")... and the officer looked at my car with camping equipment for more than two weeks... and I was sent to have a bit more of a discussion with an agent.
Parked my car and went in and waited. While waiting, another family was moving from Washington to Alaska... and they were having difficulties. Three vehicles, four possible drivers, though one was an older woman. One car contained a rifle and one of the drivers had a criminal record.
I got to the counter after an hour, explained, was denied entry but that could be rectified if I came back with proof of ties to the United States and proof that I had sufficient funds to be able to stay the duration of my stay without needing any employment.
So, got back in my car, got in line to go back to the US and called my parents on my iPhone (still a rather new tech). They happened to have been at the insurance company when I called, and so got insurance for the car that I was driving for Canada - and sent a photo of that insurance and their drivers licenses with the address clearly visible. Got to the US border agent who was confused that I hadn't entered Canada but was clearly coming from Canada and sat in that office for a little bit while they looked to see that yes, I was an American citizen.
After half an hour there went to the ATM and got a balance of my accounts. I had more than sufficient funds in the account, and then went back to the border crossing. It was the same agent at the crossing so I didn't need to explain again, but said I had the necessary proof (which surprised him that I got it that quickly) and had me park again and go in to the office.
In the office, the family was still trying to figure out what to do. An hour later after they decided that the brother with the criminal record was going to walk back to the US side and that they were going to pay an arm and a leg to register the rifle I got to the counter, showed my parents drivers licenses ("this is where I am going, I had some time without any responsibilities and so decided to tour North America"), the photo of the car insurance for Canada (they called that one in and verified it... again, surprised that I was able to get it so quickly), and matched the account on the ATM receipt with the account that I had for my card... and let me in with some paperwork in my passport noting that I needed to provide that paperwork when leaving the country otherwise entering again could be problematic.
Anyways... I had a great time in Canada. Loved Banff and later Waterton. Handed over the papers to ensure I was leaving at Chief Mountain. I'd love to do it again some day... the drive from Kamloops to Banff was one of the most enjoyable "just driving" days I've done.
It took a while, but trying to cooperate to the best of my ability and that new "sending pictures around" technology really helped.