Submitted to arXiv with a different title. How to make Google understand this is the same paper?
This may not be the answer you're looking for, but one solution would be to update the arXiv paper so that its title agrees with the published paper.  (You can change an arXiv paper's title by submitting a revision.)  Maybe you prefer the title from the arXiv, but using different titles causes enough hassle and confusion that I can't really believe it's worthwhile.

It's not just a matter of convincing Google Scholar.  If they supply a link to a paper with a different title, some users will assume it's an error without looking closely enough to detect that it's really the same paper.  The same issue will occur whenever anyone runs across the arXiv paper, since the first heuristic most people use to decide whether two papers are the same is comparing the title and authors.

If you really want to use a different title, you should take every opportunity to clarify the relationship between the papers.  For example, the arXiv abstract page and the first page of the article should explicitly state that it's the same as the published paper (and give the citation).  But even if you do that, readers will be confused and perhaps a little annoyed.  They'll naturally wonder why it has a different title if it's the same paper otherwise, and they may wonder what else you have changed compared with the published version.  If there are nontrivial changes, then you should warn the reader, while if there aren't, then it's not good to let readers wonder about that.