MPLS circuits will be substantially more expensive than IP delivered Internet. MPLS is generally used for private networks with geographically diverse locations. It enables carriers to send traffic across their network irrespective of the medium (T1, Ethernet, etc). Combined with virtual routing and forwarding, the customer only sees their own secure, private network.

You can do load sharing with BGP, but that is almost certainly more than this requires. With BGP you would advertise your network prefix out to both carriers and downstream providers would route back to your network based on BGP metrics. That’s not balancing because one carrier could have better metrics than the other.

For this type of load balancing, both carriers have unique IPs so it doesn’t work like BGP. The traffic will be routed out to a carrier based on the load sharing algorithm you select (or that is selected for you). In most cases these routers will load share per-session. You won’t go out one carrier and back in another because the originating IP for each carrier is different. All the traffic from that session stays on one carrier. Thats why it’s normally called load sharing, not load balancing. You won’t generally see the load perfectly balanced between carriers. One user could be killing a circuit for all the other users on that circuit. Meanwhile, the users on the other circuit don’t notice any problems.