If they haven't started processing your application, or if you didn't provide a UCI, they probably won't even be able to match the letters to the application unless you supplied them with a specific file number or whatever. Also, I'm pretty sure that in order to properly withdraw an application from being processed you have to do a bit more than just write them a letter saying you made a mistake. But I could be wrong.
In addition to that, they won't simply "delay" your application because you ask them to, they would basically toss it out and you would have to re-apply when you were ready again. CIC doesn't have the resources or the time to set your application aside collecting dust while they wait for you to sort out your life, when in the meantime there are truckloads of other peoples applications waiting to be opened. And in addition to THAT, if I were you I'd be counting my lucky stars and hoping that they don't put 2 and 2 together and decide that this ordeal is a sign that your relationship isn't genuine or that your spouse isn't quite ready to move to Canada with you yet.
I apologize if this sounds harsh, maybe it is I have no idea. I've been a little stressed lately and I guess I'm tired of reading these stories where people do things like this to their spouse when here I am wishing everyday that I could just finally be able to be with my wife and live a happy normal life. I could never even think about doing something as childish as writing CIC a letter to tell them to delay the application because I want to get revenge on her.
Ugh, again, I'm sorry, but I needed to get that off my chest. I hope you figure everything out and that it turns out okay for the both of you. I need to spend less time reading these stupid forums.