Portorosa is about a three-hour drive from both Catania (CTA) and Palermo (PMO); fly to whichever is cheaper. Transfer details are sent four weeks before departure. If you're flying long-haul, arrive a day early rather than connecting straight to the marina.
From Catania: bus to Milazzo with Giuntabus or SAIS Trasporti, or train from Catania Centrale to Milazzo or Barcellona Pozzo di Gotto, then a 20-minute taxi to the marina.
From Palermo: Trinacria Express to Palermo Centrale, then train to Milazzo or Barcellona Pozzo di Gotto, then a 20-minute taxi. SAIS Autolinee also runs buses.