They are friendly and cooperative, but they won't hold the charging space for you unless you're a guest at the hotel; eating in the restaurant isn't enough. I have charged there 6 or 7 times with no problems. I'd suggest putting your phone number on the dash and letting the front desk know that you are charging. Also, I always eat at their restaurant when I charge, to give them some business in exchange for the charge.
However, there is just one space and one charging station, and others have had some trouble with it being occupied, either by another car charging or by a gas car, so I'd suggest you plan to stop at the Cobourg Best Western, and keep Kingston as a fallback, since the other charging stations in Kingston and onwards toward Ottawa are slow. In Cobourg, there's a sign saying the charger is for hotel guests only, but I had a long conversation with the hotel manager and it sounded like he's OK with non-guests charging there as long as they are polite to the guests (even if they have parked in the charging space) and they bring some business to the hotel. The space right in front of the charging station is often ICEd, but the cable will reach 3 spaces. So eat in the restaurant if you can, or at least drop in and say thank you. And then on the return trip, charge in Kingston with Cobourg as a fallback.
Lastly, in Kingston, put the orange cone back in the space when you're done, even if it was off to the side when you arrived, to remind people that it's not a parking space. I don't think they have a cone in Cobourg.
Good luck with the trip! I've done it several times with no issues, but sadly our next trip over the Christmas break will be in the Prius, so as not to put my family through a 3-hour charging stop. And the next trip after that will be supercharged!