On the previous edition of Wrestling Observer Radio, Dave Meltzer speculated that Braun Strowman is likely going to go over Roman Reigns at the Payback PPV but that eventually Reigns will beat Strowman, likely at SummerSlam.
That would leave Brock Lesnar to face someone like Seth Rollins, Finn Balor or even Jeff Hardy at the July PPV.

Source: Wrestling Observer Radio