@scylla in CIC website it is there that to apply for open work permit I have to submit appointment and relieving letters of my current and previous jobs..
As
scylla has suggested, it is NOT a good idea to resign from your job before you are approved for an SOWP.
You do NOT have to include the relieving letter from your current employment = do not have to resign.
The documents you have mentioned refer to the appointment letter from your current employer + appointment AND relieving letter(s) from your previous employer(s).
In addition to this, you must include the NOC (No Objection Certificate = Leave approval letter from your current employer which does not mean resigning from your job) + other employment documents
Actually, more important than your previous employment records are the UCI Number + documents from your spouse