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!
My guess is that they were moved there from somewhere else. They were maybe used as grates to strain debris from the water, or some kind of heat exchanger. That area was definitely made flat with heavy equipment at some point.