Based on the information you've provided, you are most likely inadmissible to Canada at this time and have to start by applying for rehabilitation. Rehabilitation applications can take anywhere from a few months to over a year to process. Once rehabilitation has been approved, you can apply to come to Canada. Note that you should expect it will not be possible to obtain a work permit - it's pretty much impossible to get a job offer and approved LMIA from an employer which are required to get a work permit. If you get rehabilitation approved, you should focus on applying for PR (permanent residency) instead of a work permit.