Hello Raunak
There are two issues involved here. The first has to do with outgoing traffic. If your network is connected to multiple ISPs, then you have full control over which ISP will be used for outgoing traffic. This can be accomplished in several ways including IGP dynamic routing protocols such as OSPF or EIGRP, as well as gateway redundancy protocols such as HSRP. If you have BGP running on a portion of the edge of your network, you can accomplish this by adjusting BGP attributes to favour one ISP as well.
Now the technical details of how you can do this depends on the method you are using. If you are using a routing protocol, you can change the metrics to prefer one ISP over the other. If you’re using HSRP, you can change the active router to the one connecting to the ISP of your choice. You can also do equal or unequal load balancing. Here are some lessons that will help you in these configurations:
The other issue is incoming traffic, for traffic that is initiated from the outside, such as when you want to access a web server on the Enterprise from the Internet at large. This can only be achieved using BGP. You will have to use various BGP attributes to inform both ISPs of your internal IP addresses, and you can adjust these parameters in order to influence incoming traffic to take either the path of one ISP or another. More information on how you can do this both technically and in cooperation with your ISPs can be found at this post:
I hope this has been helpful!
Laz