Can you trade from Pokemon Red on GBA to Pokemon gold on virtual console?

Solution 1:

You can't trade from a cartridge to a 3DS console.

But there is a process to go around this, you need a homebrew 3DS (Custom Firmware) and if you have any tool to extract the save file from your cartridge.

The process would have to go somewhat like this:

1. Extract save file from both games (cartridge and VC game)
2. Get both saves to your PC and use a save file editor (there are plenty online)
3. Transfer your Pokemon from the cartridge save to the VC save file
4. Overwrite your old VC save with your modified one.

That would be a way to do it, is a lengthy process, but worth it if you really want to do it.