Bryan Alvarez reported on today's installment of Wrestling Observer Live that WWE is going to book Braun Strowman to face The Big Show at the WWE Fastlane event. Strowman would then win the match and go on to face The Undertaker at WrestleMania.
As noted, The Undertaker was originally planned to face John Cena at the annual event, however those plans were nixed because of Cena's injury.
Source: Wrestling Observer Radio
Admittedly, I haven't listened to the episode to see if he said it as speculation, or reported it as it is the plans, but this shouldn't really be a surprise to many people considering Meltzer reported that Undertaker/Strowman was a possibility back in October/November when The Wyatts were working with the BoD.
This Wrestlemania is just going to be... yikes. That match will surely be up there as one of Undertaker's worst Wrestlemania matches.
The only thing saving this from happening is Undertaker telling Vince he wants a real opponent and someone who can actually work.