Tadoussac is about two and a half hours downstream from Quebec City on Route 138.
Between Baie St. Paul and La Malbaie, Route 362 is a lovely alternative along the shore. Places of interest are Les Éboulements (old flour mill) and St. Joseph de la Rive (hand-making cotton paper & maritime museum).
On the inland route, notice a line of higher mountains to the west. This is the western rim of the 350 million year old meteorite crater which you are driving through. (The eastern edge is on the other side of the St. Lawrence River.)