United States Champion - Andrade
Rey Mysterio hasn't had fruitful reigns as a Champion lately. He won the US Championship over the summer from Samoa Joe but relinquished it back to Joe. They then put the belt on Ricochet but he quickly lost it to AJ Styles.
The Phenomenal One then went on to hold the title from Extreme Rules (July 15th) to the end of November. When he (Rey) won the title from Styles at the end of November, it was thought that he'd have a longer run. Well, it didn't happen. On the day after Christmas, the Lucha legend dropped the title to the current Champ, Andrade. Mysterio is still performing at a high level at this point in his career but he should primarily be putting younger stars over (like he did with El Idolo).
Since Andrade won his first main-roster title, he should not be dropping it any time soon. He's battled the likes of Humberto Carillo and Ricochet for the last two months and will likely continue to be embroiled with Mysterio for the next few weeks.
For that reason, I think it would be the best idea to have Andrade walk into WrestleMania 36 holding the US Championship. He'll likely defend it in a multi-man match since RAW is stacked with an uber-talented mid-card. Other stars like Aleister Black and Buddy Murphy could also somehow be interjected into the title scene between now and April.