A new book from U of T Press, Constitutional Amendment in Canada, edited by Emmett Macfarlane, has been getting a lot of buzz recently (at least in my twitter feeds.)
I haven't seen it yet myself, but I note that the first chapter, Searching for an Amending Formula: The 115-year Journey, by Nadia Verrelli of Lakehead university, is explicitly historical in focus, so worthy of noting here.