Water level is great on the Ottawa at that time of year for the main channel,it should be around 0. Water is starting to get colder, but depending on how warm a summer we get, it should be very reasonnable(compared to right now). Air temp will determine if you need dry top or not.
Weather: You could have sunshine and +25 celsius all week or rain and +10, that is unpredictable at that time in our tempered climate…Colors or trees will be awsome though, our maple leafs are just incredible at that time, great for picture background.
Busy, no, you should have the place to yourself during the week, and a few friends over the weekends. Rafts are done by then.
Boats, I doubt you can still rent a boat at that time near the river but Ottawa is just an hour away and you have tones of places you can get them from.
Any ways, have a great time(hard not to on the Ottawa) and hopefully paddle together one day (look for a Robson blue CU fly open boat, not many of those…)