Hello Anoop
First of all, we have to specify what kind of traffic you want to achieve this for, incoming or outgoing? Remember that you are in complete control of your outgoing traffic, but you are not in control of your incoming traffic. You can talk to the ISPs that you’re connected with and ask them to help you achieve the kind of load balancing you’re searching for, but there is no way to guarantee incoming traffic on a percentage basis.
Now for outgoing traffic, there are several ways to do this. These are not limited to the use of BGP but may use other connectivity methods as well, and this will depend upon your topology and your edge network architecture.
When using routing protocols for load balancing on Cisco devices, CEF is used. CEF can use either a per-packet or per-destination load balancing mechanism, so there is no way to specify a percentage. The only exception is EIGRP, where you can use the Variance command to specify how much traffic goes over each possible link.
The other option is to use shaping or policing to specify particular traffic patterns.
I hope this has been helpful!
Laz