Dictionaries tell us that the interjection/exclamation hallelujah is pronounced ˌhælɪˈluːjə (or -lə-). However, this is a word probably more often sung than spoken, and we all know that in singing strange things happen to pronunciation.
From the point of view of English, hallelujah is a strange word anyway. Apart from foreign proper names, it is the only word in which the spelling <j> corresponds to the pronunciation j (palatal semivowel). It has an alternative form, alleluia, which comes to us via Greek rather than direct from Hebrew and lacks this spelling oddity.
In the choir I belong to we are already gearing up for our Christmas show, and one of the works we will be performing is Handel’s Hallelujah Chorus, which is why I am thinking about this word. (The title itself is phonetically interesting, since it normally undergoes so-called stress shift to ˈHallelujah ˈChorus, in accordance with the usual rule.)
One thing that happens in singing is that vowels that would be weak in ordinary speech tend to become strong. So the second syllable of hallelujah is sung with eɪ (or an italianate monophthongal e), the final syllable with ɑː (or a).
The other thing that happens is that suprasegmental features (length, stress) have to be modified to fit in with the music. In Handel’s masterpiece we mostly get the usual (ˈ)halleˈlujah, but sometimes the special stressing halˈleluˈjah. In the fragment below, from the score as adapted for male voices only, you can see that at one point, while the tenor 1s and the basses are singing reigneth and the baritones have rapid normally-stressed hallelujahs, the tenor 2s stress the le syllable.It all sounds magnificent. If you’re in or near London, do come and hear us in December.