What cheese can be substituted for Romano cheese?

I would suggest either Parmesan-Reggiano or Grana Padano cheese. Both are from Italy, made with cow's milk. Grana Padano is milder than Parmesan. Whatever you choose, don't use the green can!!! It's like sawdust!

Cow's milk hard cheese from Italy, notably Parmesan or Asiago. These will give a similar taste and texture to the finished dish, but not the sheep milk taste you dislike.

Milder cheese, also from cow's milk. These will somewhat change the dish, but still taste very good:
*American (varieties of Jack cheese, Monterey Jack, etc
*Netherlands, Edam or Gouda
*Denmark, Havarti