Frankly, I wouldn't bother with GPIB or CAN ..
Use standard serial port (RS-232) or if you want to connect more devices you can implement half/full duplex RS-485 (one/two twisted pairs respectively) ..
If you use off-the-shelf termnal software such as for example:
h**p://www.rfinnovations.com.au/Uploads/Images/RFI-Interm%20Rev1.1(1).zip (change ** to tt, copy and paste the whole thing to the address icon)
you can write ASCII or HEX strings as commands and send them to Interface Box by clicking on single button ..
Regards,
IanP