I highly recommend Captain Tony's in Cabo. It's right at the marina, and it's delicious! The grilled, bacon-wrapped shrimp are my fav, but anything you get is good. And the tacos and margaritas are quite affordable!
And you'll have no problem finding a boat to the arch. If you have time, I recommend having one drop you off at Lover's Beach for an hour and hanging out a bit. You can see both the Pacific and the Sea of Cortez from the beach, and it's a beautiful, sandy spot to wander, people watch, and take pictures.