Any advance booking for a 7seater taxi from guangzhou airport to Tianhe East Road?

There is no 7 seaters taxi in the city for your choice. Then you would have two options:
1. If you have booked a hotel on Tianhe East Road, you can ask your hotel to arrange a van for you.
2. You can turn to an agency for airport pick-up service. If this way helps, I recommend Travel China Guide to you. They offer great service and the charge is reasonable. Here is the contact by the way: bookingtravelchinaguide.com
May help!