Another idea...if google brings up too many different varieties besides the native species...see if you can find a copy of Native Trees of Canada at the library. Can't remember who the author is now and I don't have a copy of it myself.
Really though, besides satisfying your own curiosity about the species you don't even need to know. Knowing the name won't likely help you much if it's a native species, the nursery's probably only carry ornamental varieties. Anyways, if there are others growing in the bush nearby you should be able to find some saplings to transplant. You can just call them your mystery trees
Most trees transplant best in the cooler weather when the ground has more moisture. From about May onwards if you try you'll need to do a lot of watering for most trees. Poplars are pretty hardy though, very hard to kill when they're growing somewhere you don't want them. Usually they keep popping up all over the place from the roots and little shoots will sprout up from cut stumps too.