Interesting idea. Of course, that would have Manitoba become the largest province in Canada (by territory) by a long shot. The question still remains whether or not Manitoba would actually want that extra area, or if Northern Ontario residents would go from being "drowned out" by Southern Ontario to being "drowned out" by the rest of Manitoba. At least if they were in their own Province, they would have control of their own affairs.There is a "burrough" of Kenora called Keewatin, so you'd likely have some trouble with that name being adopted from other municipalities.
You'd probably find more support for joining Manitoba up to Thunder Bay, and then a new province from TBay to North Bay.