It's actually on the confirmation email that you receive after making a reservation. It says:

"Check in upon arrival is not required. Backcountry campers will be e-mailed their confirmation letter, and this letter will serve as their backcountry camping permit. Campers are responsible for ensuring they have an electronic copy or printed letter when using the backcountry."

However they don't do a good job at explaining the car situation, which like you said doesn't require any paperwork since they search based on the license plate.

I logged in to the reservation site to confirm I had correctly entered my vehicle's plate number (something I clearly remember doing). I couldn't find anywhere to do that for the specific reservation, so I checked my profile section. There I found a plate belonging to a vehicle I haven't owned in a few years. I updated it, but I'm wondering where the original booking plate number went.

Yes. Thanks "Trippy". Got it! I should have read all the details at the end of the confirmation email ...

• IMPORTANT:
Prior to your visit please make sure to check Alerts in Ontario Parks to ensure you are up to date on important advisories for your park.


• One vehicle is included in your campsite permit. Additional Vehicle Permits must be purchased and displayed for all other vehicles.


• The campsite permit holder must be sixteen years of age or older.


• Backcountry campers should hang their food out of reach from wildlife; at least 4 m above ground and 2 m from tree trunks.


• Check in upon arrival is not required. Backcountry campers will be e-mailed their confirmation letter, and this letter will serve as their backcountry camping permit. Campers are responsible for ensuring they have an electronic copy or printed letter when using the backcountry.


• Garbage collection facilities are not available at all access point parking areas. Park visitors are asked to reduce waste, take garbage home, and dispose of all litter responsibly.  The possession of any non-burnable food or beverage containers (cans or glass bottles) are prohibited in backcountry camping areas.


• Don’t move firewood – Buy and burn firewood locally. Moving firewood from places where invasive insects and diseases have been found can be a violation of the Plant Protection Act. For more information about restrictions, visit the Canadian Food Inspection Agency.

SeekingSolitude wrote:

I know it is convenient to not check-in ... even a cellphone will have satellite access in a few years.

I think the major benefit of not checking in is that you don't have to waste precious time (i.e. time in the backcountry). But the other point you bring up, that common phone technology will progress to the point where we can all have access and be tracked, even in the backcountry, makes me anxious. I'm sure it's only a matter of time before somebody, acting in the name of safety or the greater good, insists that all our movements be tracked, both inside and out of the backcountry. For centuries people have been traveling across algonquin and the vast majority have done so safely and without constant oversight via technology or whatever. But if it just saves one life then it's good to require mandatory tracking in the park. Time to pitch my tin foil tarp!

... but not yet.