To my knowledge, Etherchannel is a Cisco term while link bundling is more of a generic term. The other difference is, Etherchannel is strictly for Ethernet while link bundling may encompass other media (i.e. non-Ethernet).
If both routers support Etherchannel, yes you should be able to perform it between two routers, but since routers are L3 devices, and many routing protocols support ECMP, multiple links might be done via distinct L3 individual links rather that a L2 link bundle of some kind. Other reasons for doing the L3 ECMP links rather than Etherchannel are: routers might not support dynamic Etherchannel using something like LACP, they also might not offer extensive, if any, choices for the hashing algorithm, and ECMP is not limited to the same physical peer device.
