You have a 90 day grace period to apply for a restoration of status after it expires. It's not really like you have 90 legal days.
Are you and your employer applying to get your work permit extended? If that is a yes, you would be under implied status until you hear about the results and can continue to work.
If no and you still want to stay in Canada, you should apply to change your status to visitor as of the time your work permit expires. You should apply for this 30 days before your work permit expires but because it takes them 2 months to process, you will not hear from them right away so you have implied status again until you do. As a visitor, you would not be allowed to work so you would have to stop working on your last work permit day.