Bring 1 cup of water to a boil (either on the stovetop or in the microwave.) While water heats up, prepare the next step.
In a large bowl add 1 tablespoon cold water and the unflavored gelatin. Let stand one minute.
Add boiling water and raspberry gelatin to bowl, then whisk until gelatin is dissolved, about 1-2 minutes.
Add remaining cold water (just shy of 1 cup) and whisk well.
Transfer bowl to the refrigerator and let chill for 45 minutes, stirring occasionally, until consistency has slightly thickened. Mixture is ready once a solid film can form along the top of the gelatin. While gelatin sets, do the next step.
In a food processor, add 2 1/2 cup cranberries, chopped apple, orange. Pulse a few times until ingredients are evenly chopped.
Remove set gelatin from refrigerator. Add chopped fruit, remaining 1/2 cup cranberries, walnuts, celery, and sugar to the bowl with the gelatin, then use a spatula to toss until thoroughly combined.
Spray a 16 cup bundt pan (standard bundt pan size) generously with cooking spray, then pour the gelatin salad mixture inside. Use a spatula to smooth out the top so that there aren't any producing pieces of walnuts or fruit.
Place bundt pan in the refrigerator and chill until gelatin is completely set, usually anywhere between 3-5 hours. For best results, let gelatin set overnight.
When ready to serve, remove bundt pan from refrigerator. Place a serving dish over the top of the bundt pan, then hold the plate in place while flipping the bundt pan over (so that the bundt pan ends up on top of the plate). If the gelatin doesn't immediately fall out, lift the bundt pan up about 1 inch and gently shake downwards; gelatin should quickly fall out. If needed, you can give the gelatin 5-10 minutes to warm up on the counter to help the gelatin release from the mold.
Cranberry gelatin salad can be served immediately or stored in a sealed container in the refrigerator for up to 4 days.