The waiting time for US CBP records is almost as ridiculous as that for Canadian citizenship. 8)
The 12 month time period is just a rumour. There are people reporting waiting 18 months or more and some people claim that US CBP just ignores them. Ironically, at least one US official has said that the delay is due in large part to people flooding the system with requests for their Canadian citizenship applications.
You can try to submit an expedited request. You might get lucky, as at least one poster in this thread did, but even then they did not get it overnight. But according to the rules, you need to prove that there is a threat of imminent bodily harm to qualify for expedited processing. Good luck proving that. Moreover, if US CBP starts getting a rush of expedited requests from Canadian citizenship applicants, expect them to shut that route pretty quickly.
Eileen is correct. If you get a request for these records after your application has already been in process for an unreasonable period of time, you could show CIC proof you applied for it, tell them you don't have it and don't know when you will get it, or if you will ever get it and that they cannot hold the abscence of a document that is not available to you against you. Of course, this would then throw the probity of your Canadian border records into question as well. What good are they without the corresponding US records, except in comparison to your claimed abscences?