My husband called the Canadian Immigration Hotline and was told generally the same thing. They did mention that nothing is guaranteed and that it is up to the discretion of the individual immigration officer to either accept or reject the application package without the FBI clearance letter. They also said that there are people who do successfully send in their applications with notes specifiying that they will send in the FBI clearance letter as soon as they receive it. But again, no guarantees.
I actually just got off the phone with the FBI about my clearance letter and they told me that although the website says 13 weeks, he estimates 9-10 weeks from the time the FBI RECEIVES your request. However, other people on the forum have been saying that they've experienced 3 months of waiting, so, really nothing is ever very clear (I'm learning) when it comes to all matters immigration. =) You can Fex-Ex it to them and although they are not currently expediting request, it'll at least get to you faster. Include a self addressed prepaid Fex Ex envelope and cross your fingers that they accept your fingerprints!
Good luck!!!! We're still waiting on all of my documents to arrive and hopefully will get them sooner than later. I think we'll wait until we receive everything, just to be on the safe side. I've read too many horror stories. This process is so unnecessarily stressful but it's great to have this community.