Montresor's plot for revenge hinges on a critical fact; Fortunato believes himself to be an expert on the taste and authenticity of wine. Because of this, Fortunato will be not only willing but insistent on verifying Montresor's fictional cask of Amontillado wine, in order to prove himself superior to Luchresi, a locally-accepted expert.
He had a weak point... He prided himself on his connoisseurship in wine. Few Italians have the true virtuoso spirit.
"The cold is merely nothing. Amontillado! You have been imposed upon. And as for Luchresi, he cannot distinguish Sherry from Amontillado."
(Poe, "The Cask of Amontillado," xroads.virginia.edu)
Montresor needs to get Fortunato into the catacombs of his own free will; note that each time Montresor asks Fortunato to return, Fortunato insists on continuing to find the cask. Because of this, Montresor doesn't need to do anything drastic, such as drugging Fortunato or knocking him out; Fortunato willingly goes to his doom, assured that Montresor has only his best interests at heart. Had Fortunato not been so egotistical (and also drunk), he would have not been so eager to one-up Luchresi; however, his ego forces him to prove his expertise, as Montresor expected from the start.
The above answer to the question concerning Poe's "The Cask of Amontillado" is certainly correct in identifying Fortunato's weak point as his belief in his expertise as a judge of wines. However, it seems unlikely that his strong motivation to taste Montresor's Amontillado is merely based on a desire to prove his superiority to another connoisseur or to demonstrate his own connoisseurship to Montresor.
The story Fortunato has been told is that Montresor just bought a "pipe" (126 gallons) of gourmet sherry at a bargain price. Why is he now going to Luchesi (spelled Luchresi in some texts) to confirm the authenticity of his wine? As intended, this strongly suggests to Fortunato that Montresor would have bought more if he had been sure it was genuine and that he intends to buy more if an expert reassures him. Fortunato is interested in buying some bargain-priced gourmet wine himself. If a boatload of Amontillado sherry has recently arrived in Venice, he could easily find the newly arrived Spanish ship without going to Montresor's palazzo. Fortunato could taste the wine on board and deal directly with the captain.
The only thing that forces Fortunato to go with Montresor is that if he pleaded some prior engagement, Montresor would go directly to Luchesi, as he says (falsely) he was doing when he ran into Fortunato. Luchesi could also find the Spanish ship and compete with Fortunato in bargaining for perhaps the entire cargo.
But Montresor has no intention of going to Luchesi. He doesn't want to kill Luchesi, and the Amontillado does not exist. Montresor only says he is going to Luchesi because this forces Fortunato to accompany him to his palazzo rather than putting Montresor off with some excuse and going to find the Spanish ship directly.
Montresor expects Fortunato to be planning to sip his wine, tell him it is just ordinary sherry, then find the source and buy up the entire shipload. Fortunato is a rich man. This would be only one more injury added to the "thousand injuries" he has inflicted on Montresor. And Fortunato would regard it as "an excellent jest."
Montresor is a connoisseur himself. Poe chose Amontillado because Montresor might not be a connoisseur in Spanish wines, as he is in French and Italian wines.