You have more options if you go from Santo Domingo since both Metro and Caribe Tours have several buses every day. The bus will go to San Francisco de Macoris, Nagua, Sanchez and Samana. If you take the bus from Santiago, it will pass through La Vega, San Francisco de Macoris, Nagua, Sanchez and Samana, in other words, through much the same country. But the only way you will see Santiago, the country's second largest city, is to go there.