Microstrip and CPWG transitions on PCB
The most important design goal is to keep the wave impedance as homogenous as possible. This impedance is defined between the track and GND plane (microstrip) or between two tracks (differential microstrip pair) or between two tracks with GND plane (3 conductor differential pair). It is not easy to change from one to another.

The 1. transition between pad and track is not a problem, because it is 1) just tiny and 2) electrically short compared to your 1GHz wavelength. 

But the 2. transition is hard to do and most likely unnecessary in your case. I have never seen a setup where the wave impedance was defined between two traces on different cables, so you might want to reconsider that.

Try to find a way to route your differential signal over one cable instead. Take a 1GBit LAN cable as a reference example, because this has multiple high speed capable twisted differential pairs with well defined impedance.