My client has router 2651 connected to internet via multiple ppp link. I am going to replace this router with ASR 1002 (RP1). ASR 1002 dont have any serial port, so I believe I have to replace multilink ppp configuration to PPPoE. I am having hardtime to find documents for PPPoE configuration on ASR 1002.
The title of the question indicates that you are using multilink PPP which is used to combine several point to point serial links into one virtual interface. If the ASR does not have support for serial interfaces then you would need to replace the serial links with some kind of Ethernet. But I wonder why you think that you need to do PPPOE. I would think that a plain Ethernet (Fast or Gig Ethernet) would do what you want.
It was important to have PPP to combine several serial interfaces into one group. But when you switch to Ethernet I wonder why you would still need anything related to PPP?