My understanding is that girls could legally marry at a very young age
(possibly 12), with their parents' consent. Is this recollection
correct?  In what year was this changed?  What age was then deemed
appropriate (for example, 16 with parents' permission, 18 without)?
Have there been any subsequent updates to that legislation?  What was
and is the situation for boys and young men?

Take an average year of the five years before the legislation changed.
 How many girls actually did marry very young, between the
then-current minimum age (say 12) and the newly-updated minimum age
(say 16)?  In the five years subsequent to the change of legislation,
how many married at such a young age that they needed parental
consent?  How many do now?  Approximate numbers are fine.  Parallel
numbers for boys and youg men would also be welcome, but not
essential.

Additionally, I would be interested in the historical or political
background to this legislative and social change.  Can you point me to
an essay (in French or English) about the the feminist aspects of the
1960s Quiet Revolution or of the 1970s Parti Quebecois platform?  The
essay would need to address the specific issue of the marriage of
girls, any opposition to the proposed changes (e.g. the Catholic
Church), and how social consensus was gained.

I'm not researching for an academic essay, by the way. I grew up in
Quebec and am trying to sort out fact from fantasy in my memories.

This is my first attempt at posting a question with Google Answers. 
(If I get the information I am looking for, I will also ask about
demographics.)  If any parts of my questions above are not clear,
please ask me.  If any parts are impossible to answer, I would be
happy to pay for a clear negative, that is, an explanation of why,
with your sources.

I propose to pay $10 for a sufficiently complete answer to each of the
three paragraphs that begin this posting, for a total of $30.

http://www.csf.gouv.qc.ca/fr/publications/?F=affichage&ma=20&choix=1&s=20

Thank you, reinedd-ga!  The time-line essay you found is fascinating;
I knew most of the general history but very little of the detail.  It
doesn't seem to address the issue of age at marriage, though.

Brainybabe, 

This is the only other question, which you've asked (that is, other
than http://answers.google.com/answers/threadview?id=450876 - which
does not adhere to the TOS, and therefore might be removed). You
claimed on that question that what you received here "didn't yield
what you needed". All I can see is Reinedd's comment, which is a
comment - not a full answer.

Your question has not been answered yet. It is not up to me to
speculate why. It is possible, that the information that you're
looking for is very difficult/impossible to locate, or that it would
take much more effort than usually associated with your price (as high
as it currently is).