I was given a 250-year-old anonymous Italian manuscript to work on by its owner some time ago. I did research on it and transcribed it. I provided the owner with the transcription and the result of the historical research, copy of a public lecture based on the ms., and breakdown of the content. My intention was to eventually publish the text of the transcription with an introduction, explanatory notes, etc. The author of the ms. remains anonymous. I have just discovered that the owner of the ms. has sent copies of the transcription - my work - to at least two other researchers. When I objected to my work being distributed without my permission, I was in effect "forbidden" to continue working on the project. The question is: to whom does the transcription belong? To the owner of the manuscript or to its author (me)? Is the owner in fact breaking copywright law by distributing my work without my permission?
The first question is whether the transcription actually enjoys any copyright protection. The transcription itself is a copy of a work in the public domain. In general, the only elements of the transcription that would be subject to protection are those that arise from your creative activity. For example, if you translated the transcription, the translation would be subject to copyright protection. Consider what the product of someone else's transcription would look like: would it be possible to distinguish it from yours?
I don't know whether such a test would actually be useful in court, however; it's more of a thought experiment. In fact, I should note that I do not have any specific knowledge of Canadian copyright law, and in particular I am unfamiliar with how Canada treats copyright protection in new works derived from public domain materials.
Based on a fairly cursory reading of Authorship and ownership in copyright law in Canada on Wikipedia, and assuming that you were not working as an employee, you own any copyright in the work you produced. This would certainly be true of the other items you gave to the manuscript owner: "the result of the historical research, copy of a public lecture based on the ms., and breakdown of the content." As noted above, the extent to which it is true of the transcription itself is not clear, but it is probably a small extent.
If you did the work as an employee, then the copyright in the work is owned by your employer, unless there is an agreement to the contrary. However, "employee" does not include freelancers, so the owner of the manuscript does not own the copyright in your work simply because he or she paid you.
I would also note that I don't see any way for the manuscript owner to prevent you from "publish[ing] the text of the transcription with an introduction, explanatory notes, etc."
I hope someone who is more familiar with Canadian copyright law will answer, but to get a reliable answer you should ask a lawyer with a practice in Canadian intellectual property law.
A transcription constitutes an original creative work. The sequence of words underlying the manuscript is not protected by copyright because of the age of the work, what is protected is that which results from creatively deciding which modern letters are present in the manuscript. It is not just brow-sweat that gives protection to the transcription (as would be the case of someone writing out an article from today's New York Times). However, the circumstances under which you created the transcription would matter, whether you have a contract assigning ownership of the transcript to the manuscript owner. The section on ownership of copyright says
Where the author of a work was in the employment of some other person under a contract of service or apprenticeship and the work was made in the course of his employment by that person, the person by whom the author was employed shall, in the absence of any agreement to the contrary, be the first owner of the copyright, but where the work is an article or other contribution to a newspaper, magazine or similar periodical, there shall, in the absence of any agreement to the contrary, be deemed to be reserved to the author a right to restrain the publication of the work, otherwise than as part of a newspaper, magazine or similar periodical.
(Moral rights adhere to the creator, period, but that doesn't seem to be your concern).