If you cancel your renewal process with employer A, you are not under implied status any more. You would have to quit working for employer A and would have to leave Canada 90 days after your work permit had expired.
Keep the renewal process running and keep working for employer A but at the same time ask employer B to apply for an LMO. I do not know how long it takes to get one. You have to ask Service Canada where you live.
After you get the LMO, you can apply for your new work permit. If you are TRV exempt, you can go to the border with your LMO and get your new work permit instantly. If not, you can apply on paper rather than online, see here processing times: http://www.cic.gc.ca/english/information/times/temp.asp
only 20 days for a work permit with a new employer if you apply on paper.