Went to a camping in the Laurentians in Québec (Ste-Agathe) and there were those things near some camp sites. The sites are only accessible by footpaths. No car access. And if you bring a bike, you have to walk it up a hill, so I doubt they are bike racks.
EDIT: I have sent an email to the park and they have been kind enough to reply. It's just a type of fireplace with a grate. They didn't give more info than just this. Thanks to everyone for pitching in!
This is to make sure your carry on fits on the trail (jk)
Is the area prone to bears? Could be the remnants of a small bear box for a cooler or something that went over it, either some sort of information kiosk or storage/waste box that's no longer there.