The easy way is to masquerade all outgoing traffic, and setup an ECMP default route. This does, however, rob you of the ability to use routable IPs internally.
The nice way, if your ISP will play this game, is to arrange for a dynamic routing protocol feed, and let ECMP self-generate on both routers. Doing this will allow routables to work, and will also automatically create nice redundancy (droping a link won’t drop connections, if done right).
Both work well, and we have quite a few customers doing these. If a customer is willing to throw a little extra cash at us, we will happily give them a feed. The easier, but less powerful NAT method does not require ISP cooperation.
I thank you again for the answer. I understand what you are saying. The provider says that have done Muli-link PPPoE with other customers, so I guess I need another router in front of my MT box?