Can you upload CAD drawings to a Garmin handheld GPS?

The CAD drawings wouldn't work directly.

But if you could convert the GPS info in those CAD drawings to a format like KML or GPX, then the GPS could import those and display the info on its map.

This is something that a good computer programmer could probably figure out how to do. It's maybe even possible that the CAD package you have is already capable of doing it.

KML and GPX are two popular file formats for GSP data such as points and routes; many GPS devices and GPS services are compatible.