I have an anecdote to offer. I live in the US. I recently renewed a lapsed 5-year Canadian passport. in 2009 shortly after it was issued, I received a call from Passport Canada apologizing for the mistake, but they had given me a Male designation on my passport. The representative asked me to send her the passport as soon as I could so that she could fix the mistake. I was due to fly to Canada a few weeks hence, so I didn't send it. And then I forgot about it. During the course of the 5 years, every time I remembered was when I needed it to travel to Canada, so it was not the time to mail it in and wait to have it corrected. I have flown to Canada and driven across borders multiple times per year. NO ONE has ever even pointed out that my passport gender was "M"! (and no, I don't look like a guy. :p)

People can be sticklers when citing rules, but in practice it is another matter.

Also, Sandra has a good point. If your passport and ticket indicate "M", then there is no issue. It is not up to the CATSA to comment on your hair length or clothing choices. People change their hair length and color, men grow and shave beards, etc.

FYI, the exact wording of the law is as follows:

http://laws.justice.gc.ca/eng/regula.../FullText.html

5.2 (1) An air carrier shall not transport a passenger if
(a) the passenger presents a piece of photo identification and does not resemble the photograph;
(b) the passenger does not appear to be the age indicated by the date of birth on the identification he or she presents;
(c) the passenger does not appear to be of the gender indicated on the identification he or she presents; or
(d) the passenger presents more than one form of identification and there is a major discrepancy between those forms of identification.

(2) Despite paragraph (1)(a), an air carrier may transport a passenger who presents a piece of photo identification but does not resemble the photograph if
(a) the passenger’s appearance changed for medical reasons after the photograph was taken and the passenger presents the air carrier with a document signed by a health care professional and attesting to that fact; or
(b) the passengers’s face is bandaged for medical reasons and the passenger presents the air carrier with a document signed by a health care professional and attesting to that fact.
I think the intent is to prevent a person from using someone else's passport as their own for nefarious reasons. If a transsexual has had FFS, is on HRT, and no longer looks like her old photo, yet she has not had her gender marker legally changed, could she not have her passport photo changed while still retaining the "M" until such time as she can legally change it to "F", plus carry a letter indicating that she is undergoing transition? I don't take it that the law is preventing someone from appearing in the manner they choose.