More detail, and a picture, would be helpful.
There is a number of different species of mulberry, I believe all are hardy enough for southern Ontario, the leaves are of a similar size and shape, but the trees vary in size and the fruit can be red, pink, white, mauve, purple or black. It's probably fine to eat - as you seem alreay have tasted it without ill effect, we can probably assume so; I'm not aware of any similar looking berries that are poisonous.
