Profile review - MBA in Canada & switch from Advertising to Marketing

Hello and thanks for your post.
The application process is truly holistic, and committees will look at your stats (GPA and GMAT), work experience, and extracurriculars.

You did not mention your GPA, but as far as your GMAT, if you hit your target score of 710, compared to others in your demographic, it is about the average of the schools you listed. It would be impressive to increase your score 100 points from a 610, so if you can do that, you should be proud. But even so, I suggest taking it additional times to reach your maximum potential. You have nothing to lose since schools will only look at your highest score. And even a slight increase can boost your profile. If you do not reach a 700 though, you may still want to illustrate to the schools that you have the academic ability to succeed in the classroom. You could showcase your quant ability in your resume, your recommenders could do the same in their recommendations, or you could even take a supplemental course such as stats or calculus.
It is hard to gauge your work experience without knowing your accomplishments and impact you have made there. It is nice to see that you have been promoted at least once per year. I do not feel that your advertising background would specifically hurt your chances. No matter what industry your work experience is in, it’s more important to show you have made an impact and demonstrated leadership there. Ideally this will be supported by strong recommendation letters as well. It will also be important to explain why you want your MBA, and to also illustrate the skills you already have which are transferable. Be sure your story makes sense, and is realistic and specific.
Regarding extracurriculars, make sure to really emphasize your leadership roles you have taken on. It sounds like you can do that through your time as part of the organizing committee.
Lastly, you will have to explain why you have the 8 month gap on your CV in the Optional Essay, but if you do that concisely and discuss your development during that time, it will also not necessarily deter schools from admitting you.
If you continue to strengthen your profile, you do have a chance at some of these schools, but they will be competitive, and each school simply does not have the room to admit all the world's qualified applicants. It will even be that much harder to earn a scholarship. For that reason, I suggest apply to several schools, including reach, target and safety. So consider some schools lower ranked in Canada than the ones you listed. Hopefully one of the schools you apply to will see that you have a compelling story and are someone who will add value to the classroom and community.
Good luck!