I also saw those and wondered what the heck they are. Some sort of communication equipment? How could an RCMP officer not know what they are? I think that was just their way of not wanting to tell you.
They seem to be located at major gates in the fence. They are also connected to a portable power source on the ground.
My guess is some kind of motion sensor for when the gate is closed (although one would expect there are enough cops around that there'd be at least half a dozen hanging around it anyways).