What's the Right Way to Pronounce This Baby Name?
While it's tricky to pin down, "Leena" (as in Lena Horne or Lena Dunham) is much more frequently used in the U.S. and Canada, while "Layna" is standard in Europe and Australia. So if you live in North America, you could use the "more common here" argument to break the tie in your favor.
However, both pronunciations are accepted and workable wherever you are. It's a tricky problem that besets some lovely names like Lucia and Helena (each has at least three accepted pronunciations!), Leila and Anna and Carin. And that does leave you a little stuck. If you are both truly fine with the pronunciation that prevails where you live, then you can choose that one and be all set.
If you both feel your way is the right way, though, you'll need to reconcile your differing pronunciation preferences. It’s not fair to ask your friends and family, and especially your child, to do so for you—which is what will happen if you avoid settling this ahead of time.
Many couples have trouble agreeing on a name in the first place. You're one step ahead of that, as long as you can come to a mutually acceptable decision on pronunciation. Good luck!