I am a US citizen visiting Toronto. I have a job interview with a company here in a couple of days. If I receive a job offer and they're willing to sponsor me, what are my very next steps and how long should I expect the whole process to take (from job offer to approval and re-entry with work permit)? If a company has never sponsored a foreign worker before, will I need to file the paperwork for a LMO?

Thanks in advance for any response.

The details of your qualifications and of the job offer will determine the requirements for a work permit and whether or not a LMO is required. Please refer to the Canadian work permit FAQ for more details.