Opera isn't open source anyway, so it cannot just be "ported".
Ah, but Opera *Mini* is a Java app. A reasonably complete Java Virtual Machine could do it. I know Tao did a lot of work on this, but I am not aware of anything being released that could run on Classic Amiga, or for that matter, at all.
Java never caught on as a super-duper web scripting language (it was supplanted by server-side code driving AJAX, a library kit that papers over all the brain damage in MS IE), but it does seem to be successful for cross-platform apps (it papers over the brain damage in Win32). It sure would be nice to run a java-based Palm-pilot suite or Quicken clone (called Moneydance) on AmigaOS.