Recently I've been asked by several people about their chances of cancelling a Buyer Agency Agreement.  My response has not, I'm afraid, been too encouraging.  I've had to say that they've committed themselves to a document that's, in effect, as legally binding as a Listing Agreement.  Accordingly, unless they make enough of a fuss, the odds are against them and they'll have to wait things out through to the expiry date (which I can only hope isn't as far into the future as, unfortunately, it can sometimes be).
But I think this raises the question of whether you should sign a Buyer Agency Agreement in the first place -- and even whether you should be asked to do so.  My answer in both cases -- however surprising it may seem -- will tend to be a resounding "No!"

I do sympathize with my colleagues who favour the idea of tieing people down, but I think they overlook two important points -- at least as far as activity in the residential field is concerned.  (And let me touch anon on some differences when it comes to what's called ICI real estate, which deals with industrial, commercial, and investment properties.)
For a start, there is no actual requirement for the production of a Buyer Agency Agreement before a residential offer can be made. Instead, a "Confirmation of Co-operation and Representation" form has to be completed and signed by the buyer, the seller, and the listing and selling agents involved in the transaction.  This clearly sets out the inter-relationships among the different parties and serves, if needs be, as legal confirmation of them.
Into the bargain, I think it ought to be recognized that  a Buyer Agent is only one person and, unlike a Listing Agent, doesn't have several hundred other people working for his/her client, which is the case when a property is listed with the local MLS system.  It therefore seems to me to be somewhat unfair to limit the client's options if the Buyer Agent's service doesn't live up to expectations.

As I've implied, I do ask some of my commercial clients to give me a signed agreement, but this is mainly because the practice is fairly well established when dealing with ICI properties.  Moreover, many business owners prefer to keep their interest in selling hidden from the public at large.  Rather, they choose to enter into exclusive or open listings that are made known to only a relatively small number of potential buyers.  It's also quite common to have buyers give a written undertaking to treat information with strict confidentiality when it's disclosed to them by the seller.  In fact, many sellers won't impart the details of their business without such an agreement.
However, these are circumstances that rarely, if ever, apply to the residential field -- and, when they do, the answer, at least in my opinion, lies in a similar use of an exclusive or open listing.

I must admit that I discuss the Buyer Agency Agreement idea in my website and mention that the Canadian Real Estate Association is keen to see it adopted.  I also offer a simplified version of the official form.  My purpose, though, is more to explain the need for a clearly established relationship with a buyer than with a thought of forcing someone to let me take care of them.   In fact, if the truth is told, I seldom ask my residential clients to sign one (and, for that matter, I only suggest it to my commercial clients when we're looking at non-MLS listed properties).  Instead, I rely on earning people's trust by the interest I show in helping them make the best possible buy.  Moreover, I find that I rarely lose the chance of earning a commission, even if clients stumble across "the one right house" on their own.
My experience has told me that all that's really necessary is that I make my position clear to the people who contact me:  that I fully intend to work for them as opposed to the seller and hope that, in return, they will allow me (and me alone) to prepare, present, and negotiate any offer they decide to make.  Into the bargain, I believe that, if they think I'm not measuring up properly, they should feel free to find someone else who they think will do a better job of looking after them.