WrestleMania looks pretty hard to book all the talent in right now.. If we assume every title is to be defended:
Brock Lesnar (c) vs. Roman Reigns - I'm sure it will stay a Singles Match.
AJ Styles (c) vs. Shinsuke Nakamura - Again, Singles Match. It'll be better than the Lesnar/Reigns match, but go on before it.
Alexa Bliss (c) vs. Asuka? - Staying a Singles Match. Everyone seems to think this is the choice Asuka will make.
Charlotte Flair (c) vs. ? - Not sure who will get the chance if Asuka picks Alexa. I think Asuka should probably pick Charlotte and move to SmackDown, because there's a lack of talent who can realistically challenge Charlotte on that roster. Rousey is RAW, so maybe they should roll with Nia Jax's dominance more and give her the match against Alexa, with Asuka moving over. Rousey will eventually be the RAW Women's Champion. If not, then you're probably looking at Ruby Riott w/ Sarah and Liv to give some kind of believable chance that she could lose. The likes of Naomi, Becky, Natalya are all out of the picture for beating Charlotte for the title now. The only other option is to maybe have like a Six-Pack Challenge for the SmackDown title, as it gives the whole 'even odds' against the Riot Squad kind of feel.
The Miz (c) vs. Seth Rollins - This will no doubt become at least a Triple Threat, probably more. Elias will be a strong favourite to be involved.
Bobby Roode (c) vs. ? - Again, I think this will have to include a minimum of three superstars. Ziggler, Corbin, maybe Rusev or Randy Orton?
The Bar (c) vs. ? - Would have to guess maybe the Revival? If Jeff Hardy recovers from his shoulder injury, maybe they do the 'Woken' Hardy Boyz? I can't see Titus Worldwide or even a potential Balor Club angle happening now.
The Usos (c) vs. ? - Probably the Bludgeon Brothers, but at least SmackDown has a few more realistic options. Rusev Day or the New Day returning are possible. At last one of these Tag-Team Matches probably needs to include more than two teams, as so many straightforward matches just gets a bit samey IMO.
205 Live and any NXT stuff will be on the pre-show.
HHH & Stephanie McMahon vs. Kurt Angle & Ronda Rousey - Obviously happening.
So, that's nine Main Card matches already which, not including Promos / Breaks / Interviews / Hall of Fame etc is going to take up around 2 hours 30 minutes? There's also some pretty big names without a match yet from that list such as: Braun Strowman, John Cena, The Undertaker(?), Finn Balor, Bray Wyatt, Samoa Joe (if fit), Dean Ambrose (if fit), Chris Jericho(?), Jinder Mahal, Kevin Owens, Sammy Zayn etc.
Obviously, some will find storyline matches such as maybe Owens vs Zayn at last, John Cena vs. The Undertaker if it can happen. But at the moment, the Andre the Giant Memorial Match seems like it will have a lot more talent in it than it usually does. Not even mentioned all the female stars who likely can't fit many extra matches in because both titles need to be defended. Bayley vs Sasha is likely, but what about the rest of SmackDown? They probably need a female version of the Andre the Giant Match to give them all something to do.
This is the issue with having a plethora of Mid- to Upper-Level talent, where being in a match for the IC/US Title seems a be demeaning while they don't really have a realistic chance of being in the Main Event yet either. It's difficult to find them things to do. We're going to have 12+ Main Card matches and at least four on a two-hour Pre-Show which likely have to be the Andre Match, the 205 Live Match, a Women's Match and either a Tag Title or US Title match, or some random match.