Detroit to Niagara Falls via Canada, what to expect?

I personally would stay to the 400 series highways to Lincoln Alexander to Red hill Valley to QEW to 405. They are all freeways and will be easy driving and low traffic. You will likely hit traffic in the last 20 miles before Niagara Falls, but there really is no good alternative, too many small towns, too slow etc. I would try to avoid the Red Hill Valley to 405 stretch on the QEW at afternoon rush hour though.