Hi,
Bundling several PPPoE links does work but it's not officially supported (please contact your local account team to have lattest info about the roadmap).
The main restriction is to use a single ISP for all the connection which support this feature as well so you need to contact it.
A simpler solution is to do cef load-balancing by configuring two different dialer interfaces (one per link) and having two default routes in the routing table.
HTH
Laurent.