In WPF you should want to override the function DrawTileCore.
1. The canvas here is DrawingVisualGeoCanvas. DrawingVisualGeoCanvas drawingVisualGeoCanvas = geoCanvas as DrawingVisualGeoCanvas;
2. In WPF each tile is a standalone control, so the DrawTileCore works for each tile. If your logic is works for entire map, please modify it to suitable the drawingVisualGeoCanvas.CurrentWorldExtent.
Wish that's helpful.