What time is your ADR? If early, a taxi (if you don't have your own car) may be the only practical way.
Other options are bus to MGM and then boat (or walk although it will be a fair hike to BC). The boat takes ~25 min so allow plenty of time.
Or if you are going to Epcot that day or have park hoppers, take bus to Epcot, enter and walk thorugh Epcot to the International Gate and exit and BC will be a short walk to the right. But you need park admission to do this and it is a fair walk though Epcot. Either way I think it will take at least an hour to get there. (Adding up the times from my Passporter to walk through Epcot to Beach Club is close to half an hour.)