First off I'm not sure how local le would feel about it, and they may keep a close eye on that kind of infrastructure these days, but there's numerous power line cuts that run through very isolated spots.
Get on Google Earth and check out the main power line corridors for the opportunity to shoot over 1000m. I'm not sure about west of Hwy 35, but between it and Haliburton is a main corridor that runs from just south of Minden, all the way to the Ottawa Valley. You can access it from Hwy 118 just east of West Guilford, and Hwy 127 near Whitney. If you have a sled or ATV even better as I'm sure it wouldn't take long to get to a spot where there is no one to bother. There is plenty of small corridors that follow access roads or cut cross country for short distances, but frequently more than 1km. I have one right behind my house, max range from good firing position to furthest solid back stop is 973m according to Google maps. There's a few reasons I don't use it but I have other spots I can shoot to about 300m. There's also a few corridors off Hwy 62 north of Hwy 7 and at least one of them also runs across Hwy 41 (for those in the Kingston/Belleville/Trenton area, lots of options with all the farms/open private property North/South of Hwy 7 though).
Using Google earth is great because you can see camps and cottages that you can't see from the ground. It'll save you from dealing with some guy who thinks your bullet is going to magically ricochet around, or bore through 500m of rock and forest. If you're far enough away from people and pick up everything I'm sure you won't be bothered.
Here's an example.
https://www.google.ca/maps/@45.1599444,-78.5029032,3931m/data=!3m1!1e3?hl=en
