There is a section at Cannock called “Pain in the Hardtail” (or something like that). This may give you some clues as to which bike you should take. Now before the hand-wringing “you-can-ride-it-on-a-hardtail” brigade chip in I will say that of course you can ride it on a hard tail. You can ride it on a rigid single speed if you’re keen. However it’s not all bike park smooth and groomed like some modern trail centres are. It’s pebbly and rough in places; not so rough you need suspension, but rough enough that you’ll need to be out of the saddle on a hardtail to not get too battered.
As for braking bumps, they are prevalent. Cannock does have quite a few berms of various sizes and you’d have to be going really really slow on the approach to not need any braking, or a riding God. Unfortunately too many people leave it too late to brake and the bumps get bigger and bigger.
It is a fab trail centre and worth a visit, but a 6 hour round trip from Portsmouth sounds a bit keen when there are so many other arguably better locations to ride that are similar distance or nearer.