Leinster defeated the Cape Town-based Stormers 20-11 in Dublin, while the Bulls came from an 18-point deficit to defeat hosts Glasgow Warriors 22-21 in Edinburgh.
Leinster defeated the Bulls 32-7 in last year's final, with the latter having appeared in three of the last four deciders and lost every one. They are still seeking their first title.
Two Kyle Steyn scores and a penalty try had the Warriors 21-3 in front inside 25 minutes, but the Bulls’ power at set-pieces saw them grind down their opponents and claim the ascendancy.
Tries from Johan Grobbelaar, Embrose Papier and Francois Klopper put the Bulls in front and they could even afford a rare off-day from the kicking tee for Handre Pollard, who missed several routine shots at goal.
The Stormers were in the contest in Dublin, trailing 13-11 with 11 minutes remaining, but a red card for Ruan Ackermann for a dangerous clear-out at the ruck and a yellow for Salmaan Moerat for cynical play ended their challenge.