I'm trying to find out if this is a rock or an egg

[JellyfishDiploria]

[Ludwigia]

This is a concretion and not an egg. The chances of finding a fossilized egg in Ontario's Paleozoic rocks and glacial till is anyway next to nothing. Here is a helpful link explaining in depth about Ontario's geology.

[Rockwood]

I agree that this is not an egg.  But the way it's crumbling makes me think it could be a glacially shaped chunk of gabbro.