I'm not sure I've ever seen any in Lake Ontario itself, but there are quite a few species near lake Ontario. At least three species that I've seen (U. macrorhiza, and at least two other species I haven't had as much luck identifying) and according to Carnivorous Plants of the U.S. and Canada, others are native as well.
You do have a point though. That may have happenned in Washington State with U. inflata. I misread you post, I thought it was something you had heard had happened, sorry. It is something that could, indeed, happen, and Utrics are plants that can do that, especially the aquatic ones.
You definitely have a point about the D. capensis, especially. If it can survive in Niagara Falls until the end of December (maybe longer, it's still going, I didn't have time to transplant it when I was home), and it can grow from seed to flowering in one summer in a bog, it certainly could become established, even that far north. It really does make me wonder, about what plants can do that, and are common enough to get out. Thank you for the interesting hypothetical question.