Hello,
You can make use of the below article.
https://www.safaribooksonline.com/library/view/screenos-cookbook/9780596510039/ch17s02.html
To prefer one ISP path over other, you can use local preference as mentioned below:
https://www.safaribooksonline.com/library/view/screenos-cookbook/9780596510039/ch17s12.html
Regards,
Rushi