Is this a serious question? One is a new IP on a user base half the size of the other, which is getting a new release in a major series. God of War will outsell SoT by a mile.
I suppose it is theoretically possible that SoT could get amazing reviews, and ride its streaming success into mega-sales. GoW could, in theory, get shit reviews, release along side a bunch of much better games, and struggle. So, in this theoretical case, it may be possible for Sea of Thieves to be the bigger seller. This is so unlikely as to be totally ridiculous though.
I don't find that possibility 'so unlikely as to be totally ridiculous'. Furthermore, SoT has the potential to sell digitally so masively, that, unless official statements are released, we may never know exactly how much it sold.
Edit: Corrected possiility to possibility.