Right off Route 138. To get to Tadoussac you have to take the ferry from Baie St Catherine that crosses the Saguenay River. It only takes 10 minutes and doesn't cost anything.
The ferry runs all year but due to weather conditions it runs on reduced schedule in winter. See the link below for schedules.
Look out on the water and see if you can spot whales swimming as you are relaxing on the ferry
If you're driving down to Tadoussac from Quebec City, you'll have to get across the Saguenay River aboard a ferry. The 10-minute ride between Baie-Ste-Catherine and Tadoussac is free and during the day the ferries run every 20 minutes. If you're travelling at night or early in the morning, you might want to check the schedule before leaving. The ride is short but it allows you to admire the superb view of Saguenay fjord, and of the Saguenay River reaching the St. Lawrence River. Chances are you'll also see some whales swimming not far from the boat. So as soon as you get on board, just pick up your camera and go up to the observation deck to fully enjoy this quick (and free) boat ride!
We were on a tour bus the second time by auto the first trip. You must use the Ferry to cross the river. There is no Bridge.