In a heavy, medium saucepan, heat the white wine over low heat to a gentle boil. While stirring, add the cheese, a little bit at a time. Cook, stirring, until the cheese is melted and is lightly bubbling.
In a small bowl, combine the cornstarch and water to make a slurry. Stir the slurry into the cheese mixture, and simmer over low heat for 3-5 minutes, until smooth and creamy. If you'd prefer a thinner fondue, stir in more wine, 1 tablespoon at a time.
Serve hot, with the bread and apple and pear slices.