Thank you for posting Suzy,
Sorry to say I cannot identify your mower, but I do beleive the Patterson seat has been put on as a replacement from a much earlier machine.
The Patterson Brothers started manufacturing in 1850 at Richmond Hill in Ontario Canada, now it is part of the Greater Toronto area and lies to the North of Toronto.
Talks took place between Patterson and Wisner about an amalgamation, but in 1891 the two Companies joined Massey-Harris.
I have attached a few photo's from the Massey Building at Milton showing this early history.
Also I know there are two styles of 'Patterson Cast Iron Seat' the one on your mower does not have a large hole in the front point.
Your mower is certainly a very different design to many and I hope someone comes forward to identify who made it.
Malcolm.