Provided my calculation of data transfer shows that it's "doable" within 3 hours everyday. I was considering this before I was presented with Symantec BE14. Now my partner is talking about 2 BE servers with dedupe on each side and other license options that would be required, not to mention hardware, etc. It's way over original budget and I'm not sure BE is really built for this. I mean, it's one thing if I raise the budget and the solution works, but quite another if it turns out to be an expensive pile of doodoo..
The recommended way to backup over a WAN is to do optimised duplication which is probably what your partner is recommending. This involves a media server with dedup on both ends.
You'd need to use Optimized Dedupe across a strong WAN link to do this. Read the TN below for more information:
This should be the start of investigating it...as well as a test if you have the resources to do this!