It's been a long time since your posting, but I thought I'd just reply in case you come back some time.
When I was researching my own Ker family some years ago, I jotted down all info I found on other Kers in Ontario.One bunch were those of the William Ker family, which you are looking for.I have done up a little family tree for what I did find, so there are a few generations.I did not look too hard to fill in the tree details, though.
There is a tiny chance that perhaps our Ker ancestors are related, and I only say that because of what your posting says.I found the rest of the text on the Ontario GenWeb project database for William Ker in South Dumfries township (no too far from where I now live, actually).
Anyway, it says he was born about 1772 in Cumberland County, England and emigrated to Canada in 1835.My ancestor, Thomas Ker, was born about 1790 in (Penton) Cumberland County, England and emigrated to Canada in 1832 (from Carlisle), and they settled in Streetsville, Peel County in 1835 or 1836.So there is a little bit of similarity, but it is something to keep in mind in case some link ever shows up (maybe William and Thomas were brothers).
I did similar research on Kers in the Niagara Region and had been in contact with their descendents.However, that group came from a part of Scotland, and we found no relationship there.