Make Exchange Support multiple routes

I have Two Routers:

1- Router A:192.168.10.1/24

2- Router B:192.168.11.1/24

I have one CAS:

1- NIC 1:192.168.10.10/24 Gateway:192.168.10.1 (Router A)

2- NIC 2: 192.168.11.10/24 No Gateway

I have DNS & MX Record that are pointing for my routers.

1- A Record for Router A

2- A Record for Router B

3- MX Record for both Public IP Addresses

To make my CAS reachable for both routers externally so if one router is down then the clients can reach my CAS, then should I create another CAS that has the gateway to Router B?  Or what do you suggest?

Sincerely,

Tareq