Note though that this is true only for hela=entire, when hela=unbroken it wants "den/det" as usual.
Jag vill ha den hela radion, inte den trasiga. - I want the functioning radio, not the broken one.
Jag vill ha hela pizzan, inte bara en bit. - I want the whole pizza, not just a slice.
It's complicated. In many cases – like here – both work perfectly fine. Just like you can use either will or are going to in English here.
The general idea is that ska is only used for actions that can be controlled or when somebody wants something to happen (or not happen), whereas kommer att can be used in a more neutral way, when you're making some sort of prediction about what is likely to happen. It's a lot more complicated than that, but that's a good place to start.
So if I understand correctly, it's basically the opposite of English, where "going to" indicates intention and "will" indicates prediction? (It's also more complicated in English because "going to" can be used to predict based on immediately perceivable evidence, like seeing a raincloud and saying "It's going to rain.")
Swedish has a lot of overlap as well, and natives will not always agree on which option is the best in any given situation. I'd go as far as claiming that understanding the difference between ska and kommer att can often be one of the very hardest things for any learner.
Vi ska täcka hela vägen, so I heard, or maybe because the sound I thought I heard is pointing to the word I know very well, that is, vägen. Oh, a certain artist is asking all the volunteers to cover the whole road for his art project, it came to my mind.
The question here is, that "väggen" and "vägen" are quite different, right? when you look at them, sure, but when you hear them spoken, are they quite different or a bit different in a tricky way?
P.S. I just tried to confirm the differences in sound in the Duolingo Swedish-English dictionary. Between väggen and vägen, I canno hear the difference! I hear them rather the same. I am confused.