Suggestion for installing a linux router for traffic redirection

[glenntoy]

Given:
ISP-A connected through an ASDL modem through static IP
ISP-B and C connected each through an ASDL modem through dynamic IP

Current setup:
Each of the ASDL modem is connected through a router.
ISP-A ADSL modem is connected through DLINK DFL-860 (192.168.5.31) --> for making voip calls, sending small size emails and quick surfing
ISP-B ADSL modem is connected through DLINK DI-LB604 (192.168.5.32) --> for surfing, sending large files through email and downloading
ISP-C ADSL modem is connected through pfSense (192.168.5.33) --> backup of ISP-C

All workstations by default uses the gateway ISP-A (192.168.5.31). When workstation users wants to download large files they change its gateway to ISP-B (192.168.5.32). If there are problems in downloading files in ISP-B, they switch to the ISP-C (192.168.5.33).

Proposal Idea (I don't know if it is a possible):
To build a linux router (192.168.5.34) that acts as a gateway to all worsktations so that users will not be switching from one gateway to another
The linux router will be in-charge in routing all smtp, surfing and downloading to ISP-B and all voip calls to ISP-A

Questions:
01.) Can this be achieve using a linux router?
Q2.) Can this be achieve using a the combination of Ubutu server and squid?

I'm really newbie with this, but I'm hoping someone could shed a light on how to solve this matter.

cheers,
Gee

[numberwhun]

Sorry for the late answering of this questions. I am not sure, but hopefully these links will provide some kind of answer for you.

Regards,

Jeff