It is really not worth going to Italy for a day from Monaco, instead, spend more time in Nice and area around it. I’m sure you know that that area was part of the kingdom of Piedmont-Sardinia (an Italian state), which can still be seen in architecture, food and local dialects. Why go somewhere just to cross a border that’s very recent? If you want to have a good Italian meal, try Chez Acchiardo in Nice.