Survey Iron Bars
It's actually illegal to remove survey bars in Ontario, however it's difficult to enforce and it happens quite often. The good news is that the location of that corner of your property is documented on the survey plan that your surveyor gave you. You may want to ask your neighbour to pay for the surveyor to come out again and replace the bar. If they won't and you want that bar there, maybe it's a cost that you'll be willing to incur. If you don't then you can rely on the measurements on the survey plan to approximate where the boundary is.