ID: Serated-leafed seedling
An extension of com.prehensible's comment -- your sapling could be a bur oak.  It is older than the seedling pictured below, but retains a similar cotyledon.  The range of this species includes Ontario.


bur oak seedling
Photo by Todd Dwyer, via Flickr
(please ignore the image artifact -- an effect of resizing)

Your photo appears to show the tree at a stage after the seedling shown above and before the more mature sapling shown here:


bur oak sapling
Photo by John T. Fowler, Alamy Stock Photo