@MichaelMulvaney, you asked just after I had discarded my specimens so I had to go back to the trees. Photos taken 24 May showing underside of leaves and hairs on ribs. They match street tree plantings on Kitchener St. Hughes. (I can make an additional sighting complete with acorns for these if you want a comparison).
Most unlikely to have been planted, going by the location and the work done in establishing the pond and embankment in 2003. There are other weed trees nearby but they look older.