I actually think you could get longer out of Kane than Haaland. You will get a maximum contract of three/four years out of Haaland. He won't sign for any longer than that, and I doubt any extensions will happen (unless he turns out to be a disappointment). Considering the near £100m fee, I bet we will keep him for most of the contract, so the resale value will be hit. Either we accept a low fee or he leaves for free when his contract ends. Resale value will not be great for him.
I would prefer Kane. Kane is like hitting two birds with one stone, being both top scorer and top assister in the league. I mean his assist numbers may drop off a bit as I doubt he would come as deep for us, but his goal scoring should improve.
Pogba joined us and signed 5 year contract (with an additional year extension that can be triggered by the club which the club did) so this is effectively a 6 years contract, Pogba was 23 we he joined and he is 28 now.
Maguire signed on a six-year contract when he joined.
Kai Havertz is on a five-year contract with Chelsea.
Philippe Coutinho signed 5 & half years deal with Barcelona when he first joined them in 2018.
Ousmane Dembélé also igned 5 years deal with Barcelona when he first joined them in 2017.
usually, for these signings with huge transfer fees, the club would not accept a 3/4 year contract with the player, it is 5 years minimum and United if ever they sign Halaand, they would surely tie him to a long term contract (5/6 years at least).
Halaand is just 20 years old now, if he joins and is tied to a long term contract, that is not an issue, because he would still be 27/28 years and can sign another major contract with any club.