hi,
I am here in CANADA on a workpermit VISA (tied to a company) and work for the same company.
1. Is it possible to change the employer?
2. If yes, do i have to get a new workpermit while i am in Canada?

Yes, you can change employers but would be required to seek a new work permit (i.e., outside of Canada) or change of terms (i.e., within Canada, inland) prior to commencing work. You may also be required to obtain a Labour Market Opinion Confirmation for the new position.