Comparing commits on two different branches

Hi,

I have two branches - I know that one differs from the other entirely by a (large) number of commits that I have made over some time. Unfortunately, these are now all mixed up with a load of other commits that have been merged into both from the upstream project.

Is there any way that I can get the list of commits that represent the difference between the two branches? Even better is there some way that I can apply all those commits to a third branch (a newer version of the project) without having to do hundreds of cherry-picks?

Thanks!