Include your job letter in the web form and write a detailed explanation letter on how you meet all the job offer requirements, and only missing requirement is the citizenship application, As per my old link, your request would fall under this "
- the applicants are Canadian citizens and face loss of employment or of employment opportunity because they are not in possession of a document establishing Canadian citizenship
So, there is a high probability that they will fast-track your application if you already have an offer letter. After submitting the webform, call the IRCC Client Centre and ask them to leave a note for the officer to check your urgent processing request. In most cases, the officer will need to respond to these requests within 7-30 days (from what I have heard). Try everything you can, and hopefully it works out in your favour.. Good luck..