In the past, when most camping reservations were made by direct phone calls to the park of your choice, you might have had a bit more leeway. But most campgrounds now use a centralized online reservation system, and your chance of missing out increases with every day that goes by after they open that booking window.
In Ontario, where we live, online reservations open 5 months in advance for our provincial parks. When I checked this week, many provincial park campgrounds were already booked solid for the weekend that includes Canada Day, July 1st.
Campground Advance Reservation Windows
Booking windows and reservation restrictions vary province by province. Perhaps you're planning a cross-Canada trip? I've put together a quick guide on where to go and when to book individual campsites in various provinces. (Booking windows may be different for group sites, yurts, cabins, back country sites, or in other special situations.)
Canada National Park Campgrounds
Book up to 12 months in advance, starting Jan 1. Reservations can be made for current calendar year only. https://reservation.pc.gc.ca/ParksCanada
Provincial Park Campgrounds
Alberta: 90 days in advance, starting Feb 19, 2019. https://reserve.albertaparks.ca
British Columbia: 4 months in advance. To prevent the practice of overbooking all reservations made within the first 7 days of the allowed booking window will not be permitted to change arrival dates. Reservations made later won't have this restriction. http://www.env.gov.bc.ca/bcparks/reserve
Manitoba: Reservations open Monday, April 1, 2019 at 7:00 am for Winnipeg Beach and all campsites in Whiteshell Provincial Park, including Betula Lake, Big Whiteshell, Brereton Lake, Caddy Lake, Falcon Beach, Falcon Lakeshore, Nutimik Lake, Opapiskaw, Otter Falls, West Hawk Lake and White Lake campgrounds.
On Wednesday, April 3, 2019 at 7:00 am reservations open for all remaining provincial park campgrounds.
New Brunswick: 12 months in advance, starting Jan 1. Reservations can be made for current calendar year only. https://parcsnbparks.ca
Newfoundland and Labrador: Reservations opening date changes annually. The 2019 date has not been set yet, but in 2018 it was April 25th. After that date, they can be made for the current calendar year. https://www.nlcamping.ca
Nova Scotia: Reservations open on April 2 at 9:00 am and can be made for the current calendar year. https://novascotia.goingtocamp.com
Ontario: 5 months in advance. https://reservations.ontarioparks.com
Prince Edward Island: Reservations open April 1st for the following season. There's no centralized online booking system. Make reservations by calling the individual Provincial Parks directly weekdays between 8:00 am to 4:00 pm. Find the 8 parks with campgrounds at https://www.tourismpei.com/pei-provincial-parks
Quebec: 12 months in advance. https://www.sepaq.com/reservation (Provincial parks in Quebec are called "national parks", and managed by Sépac - the Société des établissements de plein air du Québec. Federal national parks are distinguished by the addition of "of Canada" in their official name.)
Saskatchewan: Reservations open dates will be staggered between the different campgrounds from April 2 to Apr 8, 2019 daily at 7:00 am. https://saskparks.goingtocamp.com
USA National Park Campgrounds
For most locations, you can reserve six months in advance of your stay for individual campsites and 12 months in advance for group sites. There are some exceptions, so it is best to check the details page for each park. https://www.recreation.gov
USA State Park Campgrounds
I haven't done similar research to provide a guide for all 50 states, but you should be able to find the booking window information on the individual official state park web sites. Find links to each of them at https://www.stateparks.org/
Not Reserving Months in Advance?
If you cannot (or refuse to) reserve months in advance, don't worry - all is not lost. There are bound to be cancellations and opportunities to luck into a cancelled site. Watching for them is a big job, though, but there's an app that can help.
Campnab.com constantly scans sold-out parks for cancellations. It then notifies you (via text message) of openings in the parks you're interested in. Based in Canada, and still expanding, you can currently use the Campnab app to request cancellation notifications for national and state park campgrounds in the USA, national parks in Canada, and provincial parks in British Columbia and Ontario.
You can always fall back on my other tips and workarounds when you don't have a reservation.
And, of course, our own wonderful hosts are a great back up plan for a night or two. None of them are booked more than 2 months in advance. Some set their maximum notice preference for even less time so there's less chance they'll be booked up when you need them, and the majority of our hosts don't mind same-day requests. They're the perfect solution while waiting for an opening in a nearby park.