Honestly, I would strongly consider Sosa over Ulissi, despite it being an unpopular opinion here.
Taking a look at the last three participations of Ulissi in the Giro, his results in those three years that would score him points in your game are:
2021:
GC: 17
Stage results: 15, 5, 4, 12, 17
2020:
Stage results: 1, 20, 16, 1
Points classification: 7
2019:
Stage results: 15, 3, 17
To me that's not overly convincing. Of course if he wins two stages as he did in 2020, he'll likely be a better pick than Sosa, but Ulissi is not a rider who often finishes in the top 20 on stages. Also, Ulissi isn't getting any younger (well, nobody is, but he's not as good as he has been), and Sosa has seem kinda reborn this year.
Of course there are a lot of question marks hanging over Sosa, and I agree with everyone saying that he's not the obvious GC rider and it's likely that he will collaps at some point. I just think that the upside of Sosa is much higher than that of Ulissi and he's riding as a captain for the first time.
Looking at betting odds, the bookmakers (I looked at Bet365) assess Sosa's and Ulissi's chances of winning at least one stage almost equal (3.25 for Ulissi and 3.50 for Sosa), while Sosa is 2.50 to finish in the top 10 of the GC (Ulissi is 51.00 to finish in the top 10 of the GC).
Anyway, that's just my take on it. If you're risk averse, go for Ulissi, if you're risk tolerant go for Sosa would be my suggestion. Again, it depends on the potential payout. If finishing 3rd or 30th doesn't really matter much, I would lean towards the higher risk-higher upside pick in Sosa, but if the payout structure is much more flat, then that speaks for Ulissi.