Two eBGP routers peer across two parallel serial links of equal bandwidth. I have configured loopback interface as an update source and eBGP-multihop on both routers.
Is here a way I could verify load-sharing is functioning accross the two parallel links?
You mean you have RouterA and RouterB with two parallel serial links and you configured eBGP using loopback, static route each router loopback, and configure ebgp-multihop?
From RouterA traceroute loopback IP of RouterB. It should show two IP Address in the first hop. http://www.cisco.com/warp/public/459/40.html
Also, you can setup an MRTG to monitor it permanently.