I paddled Tadoussac two years ago. The whale watching is superb. The water temperature is 35 degrees in August. That means you need skills to paddle this area. The tide changes are 15 feet and flow twice a day. If you are caught in an outflow, you are going to sea.
I recommend picking up a guide. Also, you need a drysuit there. It is cold, even in August.
I don't want to scare you away - just go prepared. We had seven Fin whales surfacing around us at one time. Fin whales are 70 feet long - only Blues are larger. Awesome.