From Quebec City, take the ferry to Lévis and follow Route Verte #1. If you stay on the north shore, expect traffic and monstrous hills. The Route Verte #1 follows highway 132 except through some villages and the occasional small road sandwiched between the main highway the St-Lawrence. There's a unusual very hilly bike path around St-Simon.
I enjoyed riding the bike path on the south side of the St. Lawrence east of Quebec City. Consider it if you want an easy route.
The north shore east of Quebec City is extremely hilly, and there is a lot of traffic, but the route is spectacular. There are ferries you can take to cross the river at several points.