What action should be taken, if my buyer’s agent drafts and presents my Offer to purchase, containing clauses that are beneficial to the adverse party (seller) without my express consent and not in my best interest. Have they breached their fiduciary duty?

Did you sign the offer?

They may have breached their fiduciary duties but if you signed the offer and its been accepted you'll still be on the hook for it. You can't just get out of an offer by saying you didn't read it

Your agent would have explained all the clauses before you signed the offer. At that stage you should have asked the agent to add or take off the clauses that you did not like. If you signed then you are accepting the clauses. If you feel your agent did not work for you, you can always talk to the broker of that company to resolve the issue.

I've had it happen before as well. My suggestion is just talk to your agent and try to resolve it.

You always have a legal option but that usually costs more then the actual damage.

If you have signed the Offer to Purchase you have expressed consent with your signature.
Anyway, your can file a complaint with the Real Estate Council of Ontario (RECO) and specify the allegation of misconduct.
Check this website: http://www.reco.on.ca

Assuming you realized this in hindsight; it is still your consent to express the terms of the offer. All the terms & clauses should have been explained to you before you sign the offer.

If the realtor won't stop the process, call the realtor's broker.
If you're need to make a complaint; contact the Real Estate Council of Ontario (RECO).

Competence, Real Estate Brokerages must:

have sufficient knowledge, skills, and experiences to transact the real estate as required;
exercise reasonable care to a standard expected of an average Brokerage; and
undertake best efforts to avoid having the principal act on misrepresentations, mistakes, or fraud.

Good Faith, Real Estate Brokerages must:

be honest and not take advantage of their principal;
promote and protect the best interests of the principal;
disclose any conflicting interests to the principal;
disclose facts about the property which would be relevant to the principal’s decision in buying or selling the property; and
disclose in writing to the principal if they are representing multiple parties.

Loyalty, Real Estate Brokerages must:

place the interests of the principal above all else (except the law – which means they cannot help them commit a crime, for example);
help to promote and protect the interests of the principal at all times and considering the bests interests of the principal; and
disclose a conflict (actual or perceived) between their and the principal’s interests; and
disclose in writing if they represent more than one principal to a transaction and must not act in that capacity unless they have the written consent of all principals (who have been fully informed).

Obedience, Real Estate Brokerages must:

act pursuant to instructions received by their principals (irrespective of whether they agree or not).

Many of these fiduciary duties are found in sections 2-8 of the Code of Ethics, which Real Estate Brokerages are bound by and which are made pursuant to the Real Estate Business and Brokers Act, 2002.

Individuals with complaints against Real Estate Brokerages and Salespersons can take civil or criminal action against them (depending on the nature of the complaint) and can launch a complaint under the Act to the Real Estate Council of Ontario (”RECO“). Part V of the Act deals with complaints, investigations, and disciplinary measures which can be taken by RECO.