Hiya
As I understand it, if the Halifax/Wetpac are willing to sponsor you, they would usually offer you a subclass 457 visa to start with, which is temporary but is an employer sponsored visa.
The contract generally contains a provision that they will offer to sponsor you for
PR under an ENS subclass 856 visa after a year if they are happy with your performance and you want to stay in Australia.
Most of the Migration Agents seem to reckon that this is a stupid approach from the employer's point of view because there are more fetters on the employer under a 457 visa than there are with an 856 visa.
I would suggest that you should speak with Go Matilda and maybe instruct them to correspond with your HR Department for you. Their contact details are here:
Go Matilda - Your Gateway to Australia - Contact and Feedback
However, would you qualify for a skilled independent visa in your own right? If so, then all you want from the bank is an offer of employment from Westpac - with no obligation to work for them if you don't want to.
"I work for the Halifax" is too vague, chooks! Precesely what is your role in the Halifax? Please see the following links:
Is your occupation in demand? - Workers - Visas & Immigration
Are you an accountant or an IT wizard by any chance?
Here is the full list of recognised skills. Scour it because often some lateral thinking is required to find the right skill-description and code.
A-Z Occupations List - Australian Skills Recognition Information
Workers - Visas & Immigration
Information Booklets - Applications & Forms - Visas & Immigration
Best wishes
Gill