I have been experimenting with fruit filling for a long time, seeking for the perfect consistency, which will not drip out of the cake while baking. Unfortunately nowadays in shops you can find only jams and jellies which are rich with pectin. Those do not behave well during baking, being not thermo stable. One can also buy ready-to-use fruit cake fillings, but the percent of fruit there is very low.
Also we don’t have fresh berries sold here, only frozen (cherries, raspberry, and blackcurrants).