Bayern were recently crowned Bundesliga Champions, for a second year in a row, after Leverkusen interupted their league dominance by lifting the league title in the 2023/24 season.
They are also in the semi-finals of the Champions League where they are tied 0-0 with Paris Saint-Germain after the first leg.
Kane opened the scoring in the DFB-Pokal with a goal on 22 minutes at the BayArena and Diaz wrapped up procedings with his effort in the third minute of injury time at the end of the match.
Bayern will now play one of VfB Stuttgart or SC Freiburg in the final - the two sides are set to compete for their final place on Thursday.
Speaking after the game, a delighted Bayern boss Vincent Kompany said on OneFootball: "Berlin has been talked about since the first day I arrived at Bayern.
"It's a massive gift for the club to get there again. You're always occupied with the next match, but we'll also enjoy this moment. It's about titles – and we're in the running for all of them.
"The most important thing was that we got through. The first half was very good from us – we didn't concede anything and created chances. In the second half, Leverkusen came into the game more. They forced us to defend deep because they played good football."
Kane added: "It was a really strong performance from start to finish.
"The way we played and how we won the ball back high up the pitch led to good chances for us in the first and second half.
"The only thing we could've done better is score more goals. We kept them in the game. The last 10 minutes are then always a bit nervy, of course, but overall we had control. They didn’t create many chances."
Leverkusen boss Kasper Hjulmand was naturally disappointed but conceded defeat to a "top side".
"They're a top side. They put us under pressure from the start, and we didn't find the right way to play against Bayern.
"That makes it very difficult because they keep coming forward.
"We turned the ball over a few times – there were five or six situations where we didn't handle the ball well. The pressure from Bayern was slightly lower in the second half and we were more in the game.
"The last 20 minutes were a bit better and closer, but we only had two really good attempts. Of course we want to be play bravely, proactively, but there’s also another team – and today they were very, very strong.
"A lot is decided in the one-v-one situations in particular, and they were better there."
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