TStandardCanvasModel, which derives from MCanvasRepresentation and TModel.
TStandardCanvasSelection, which derives from MCanvasSelection and TModelSelection.
TStandardCanvasView, which derives from TCanvasView.
You can probably use these classes for most of your GrafEdit programs. "Creating a simple GrafEdit program" on page 11 has an example that creates and opens a document based on the standard GrafEdit classes.