That Canyon for £870 look very good spec for the price. Especially that it weights only 8.3kg! Frame has to be pretty light as Aksiums are not that light, however good and strong wheels.
I was checking what £700 will buy you now and it looks like some bikes in that range will still have Sora although in the newer 9sp guise. I saw a Giant with alu frame and full Tiagra for £999 in a shop window the other day. Seems a bit much.
As mboy says Tiagra works really well, I used to have a Tiagra equipped Trek before swapping to Ultegra 9sp, and to be honest there is not that much of a difference in terms of performance. Probably more of a weight difference between the groupsets. Coming to Tiagra from Sora though it was a big difference as the thumbshifter on STI’s is sometimes hard to reach, does not work as nice as Tiagra etc.
At £700 I could be tempted to look for some mint condition second hand bikes as well. In that price range you could choose from some really really nice bikes, Ultegra equipped or better. Let him try some for size to know what size he needs, however with sizing, I’m 5’10” and had frames from 52 to 56cm and just used a longer/shorter stem. All fitted fine and rode fine. But be quick, season started and bikes will start to fetch silly money on eBay again. Plus always factor in around £30-50 extra for new bar tape and cables to get that new bike feel 😉