Hello @dharmendra.navar ,
are your edge routers A and B acting as PE that is they have an MP i BGP session in AF VPNv4 or they have an iBGP session in AF vrf <Internet> ?
>> Can I use ''bgp bestpath as-path multipath-relax'' command to load balance/share outbound traffic between these two service providers in different AS'es ?
The original use of the command should be to make comparable two eBGP routes coming from two eBGP sessions terminated on the same router.
Here you have two ISPs and two routers with an iBGP session in the middle.
The results may depend on the type of iBGP session they have (VPNv4 rather then vrf <vrf-name>).
You can try and report here as in the context of VRFs the distinction between eBGP and iBGP ( advertisements coming from other PE node) is not considered.
Edit:
the command may be not available in the context of a VRF but you can use the following one
maximum-paths eibgp 2
Hope to help
Giuseppe