No. There are no titles/registration required for in bed truck campers up here.
Not sure I would try sneaking it back across the border. It is really just not worth it for all the problems you may have if you are caught.
If you do try and say you were just camping, then you better be prepared to spend a couple days up here before you go back. They see the date/time you left the US in the computer and if you say you were just camping, but the computer says you have just been gone a couple hours, they will get very suspicious.
I buy trailers/equipment/trucks from the US and import them back up here all the time with little to no problem. Same goes for stuff I bring into the US for others.
Get a bill of sale with the sellers name, address and contact number (in case US Customs decides to call them) and you will likely be fine.
The BEST way to see if there will be a problem at the border is to call US Customs at the border entry where you will be crossing back into the US and asking them what they will need in terms of paperwork. I found this to be the best way, as the person you are asking the questions to on the phone is usually the exact same person you will be dealing with in person when you go through customs.
-Ask them what paperwork they need and when they need it done (some paperwork for US Customs needs to be sent to them a few days BEFORE you go get it.
-Ask when you can cross the border with the purchase. Any time I need to bring a truck over the border, I need to stop at US Customs before so that I can get the paperwork stamped for Canadian Customs. But US Customs at my entry point is only open between 8am and 5pm, Monday to Friday. If I were to try and pass on a weekend, for example, my load would be seized and held until Monday (and I would be charged storage fees during that time).
-Ask if there are any fees for the paperwork and/or things like taxes on the goods. It can suck to have everything you need to bring something back, but are short $20 for fees.