Brussels is easy... you have to hit Delerium Cafe, Cantillon, Moeder Lambic, and there's lots of other options around town. Timmermans was also a cool tour... although they are owned by the Martins hotel conglomerate , you can see some great lambic history in a museum upstairs and they also have pumped a lot of money into restoring the brewery. In Brugge, Le Trappiste is an awesome bar in a Medieval brick basement with a great selection. Fort Lapin is a cool micro/nano brewery that has the spirit of an American small brewery with great Belgian beer .
Not sure about Ireland, but they actually bottle Guinness at Timmermans from some contracting agreement! Maybe you could ask for one and skip the Irish leg of the tour. I like the Green/Yellow Spot whisky but the beer will be disappointing after Belgium.