U don’t need to extend it . SIN is just a work identity. If u r in implied status u don’t need to visit sevice canada
Banks don't need your SIN when you're applying for loans/mortgage. I never give my SIN out
But my bank already sent me notification that my sin is expiring and I need to renew it
Some point about this issue:
1-Your SIN will automatically be valid until the end of your implied status (either you hear from your work permit or your PR). You don't need to update it. Explain this to your employer. That should be enough.
2- Your Bank shouldn't need it immediately. So there shouldn't be any problem.
3- Bank generally need SIN for information about your taxes. If you have any saving account, or TFSA, or RRSP account, Bank uses your SIN number to let CRA know of your information, CRA uses these information to decide how much limit you have in your TFSA and if you need to pay any taxes. Also, if you have any saving outside the TFSA, banks issue a T5 tax slip that is based on your SIN number
4- As soon as you receive any result from either your PR or BOWP, renew your SIN number and give it to your employer and your bank. (don't give it to anyone else!)
5- If you don't have PR, you can't get any loan or mortgage.period. Then, why worry about having sin or not.
Hope these helps