Volume, there is no physical link between elevators.
The primary aerodynamic link is via the servo tabs, which are joined by independent pitch control circuits via the flight deck control columns. In the event of a jam anywhere in the system even this connection can be split. There is a secondary ‘aerodynamic’ connection via the left and right trim tabs, which are connected and cannot be split. This to some extent keeps the elevators together in flight, but as indicated by the photo other effects could cause a small asymmetry, rudder, yaw, roll, etc.
With small asymmetries the difference in force (load) on each elevator is minor with respect to the total design load, the ‘springs’ in the servo tab circuit may provide some balance. The aircraft is certificated to cope with a jam (block) of one elevator and sustain safe flight by using the other; again the loads are within the design requirements.
With the autopilot engaged only one servo tab is controlled at the rear of the aircraft (different sides for 146 and RJ), the effect of this in theory, is that the ‘on-side’ tab moves first and the ‘off-side’ tab follows up via the full length of the pitch control circuit, but in practice there are no noticeable effects as shown by the exceptional performance of the RJ autopilot / autoland system.