how much advance for Quebec City

Weekends in the summer can be pretty tight everywhere in Canada.
Our summers are too short!

Unless you can schedule your visit Mon-Thurs, I'd reserve.
Dunno about lead times though. Maybe pick a few sites and call?

We usually stay at Parc Nationale de la Jacques Cartier about 30 min north of Quebec City. Depending upon what you're looking for, they may have a few mid-week spots available.
https://www.sepaq.com/en/reservation/camping/parc-national-de-la-jacques-cartier

EDIT: Just saw your RV. Prolly the only thing Jacques-Cartier would have is an unserviced parking lot. But it's still a beautiful place. We've camped in their parking lot and had a great time.

Brulaz, thanks. no schedule yet so could set up mid week. Parking lot doesn't concern me if I can use generator at meal time. Have solar for battery charging. Just want to revisit the old city and a few of the sights I have visited many years ago. Will call a few as I get my schedule more defined.

We used "Berniers RV" across the St. Lawrance, on the south, near a small place called St. Nicolas. A bus picked us up and drove us across the bridge into Quebec City where we rode the double decker bus to tour the city - the only walled city in North America, a city since 1608, one year newer than Jamestown, Virginia. Later, after a fine lunch, we were bussed back over the bridge to our RV Park. (First week in September, no reservation.)

At the end of July last summer, we used the Quebec City KOA located at St. Nicholas. IIRC, we booked the site a couple of weeks prior to arriving and had no issues getting a site but it may not always be that easy.

Not sure if it still applies but in the past all Quebec construction workers got the same 2 weeks off in the summer as vacation across the province, it made campsites very difficult to get for us in the past. I would check and confirm, or maybe someone on the forum from Quebec can comment.

The construction holiday has varied over time. Typically vacation time is spread between the last two weeks of July and the first week of August. The actual shutdown of construction sites is a lot less the norm now due to contractual commitments.

My recommendation would be to have reservations from mid-July through mid-August and anytime covering weekends for both months.

Thanks all.

We stayed at a place called "Camping Transit." Early in the season, they honor Passport America. It is a few miles north of QC, but it's an easy drive. The owner offers a shuttle into and out of the city (To the ferry terminal). each day. We drove in, however. There is a great bike path along the Seaway beginning at the ferry terminal. We spent an afternoon there. Then we got around early and parked in the ferry parking lot to tour the city.