I was laying in my bed at six in the morning and I couldn't go back sleep so I did what every person does when this happens, I recasted the DC Universe with Marvel actors. I have too much time on my hands... but this list is great.
Heroes
Batman: Robert Downey Jr
He may not have the physique but RDJ has proven he can play a billionaire/superhero and I'd love to see his take on the playboy side of Bruce Wayne.
Superman: Michael B. Jordan
I know, I know. Crazy, right? How can I cast an actor that is barley six feet tall? All jokes a side, I really couldn't think of anyone else who could do service to the role while not looking ridiculous in the suit. I gave Chris Hemsworth and Chris Evans a chance but they fit way better with other characters (plus my Jor-El pick is money).
Wonder Woman: Brie Larson
I have no other choice.
Aquaman: Chris Hemsworth
This is probably my best pick so far. Despite Jason Momoa's awesome portrayal of the character, Aquaman wasn't always a long-haired, beer-chugging, crazy man. He was a blond white dude and Chris Hemsworth is the best blonde white dude for the job. Also, it's a smart a marketing strategy because all the ladies will pay just to see Hemsworth shirtless in the water.
The Flash (Barry Allen): Chris Evans
Just imagine Chris Evans' voice saying Barry Allen... It just sounds right. Once again, if you're going off Ezra Miller's portrayal of the Flash this doesn't make sense; however, in the comics Barry Allen is actually a little older in most incarnations and is a genius. Plus, we've seen Evans play a similar hothead as Johnny Storm in the Fantastic Four movies.
Green Arrow: Jeremy Renner
I have a feeling Jeremy Renner is going to be cast as that useless guy with an out-dated weapon for the rest of his career.
Green Lantern (Hal Jordan): Sebastian Stan
Low-key fantastic pick here. Enough said.
Green Lantern (John Stewart): Chadwick Boseman
Wait, the guy from the Daily Show? No, the black Green Lantern. Given the fact Chadwick Boseman has been butter in every role I've seen him in, I think he could pull this off.
Shazam: Chris Pratt
This is genuinely the only role I could see Pratt's comedic chops fitting with.
Cyborg: Anthony Mackie
You could go a few ways here but I went this way; Mackie plays a good fifth wheel.
Robin/Nightwing: Tom Holland
Tommy boy could also make a good Flash but c'mon, the Robin to RDJ's Batman? It's only right.
Supergirl: Tessa Thompson
A little Creed reunion here with Michael B but not sexual in this one seeing that Supergirl is Superman's cousin.
Black Canary: Scarlet Johansson
If you're not familiar with the character, I'll I can tell you is she has powers involving making noises I think and she's Green Arrow's love interest. I could see it Renner and Johansson getting along well.
Martian Manhunter: Paul Bettany
He's got the smooth voice and is not foreign to playing a different colored person with a cape.
Atom: Paul Rudd
It's literally Ant-Man.
Doctor Fate: Benedict Cumberbatch
Keeping it in the family here. I guess P.H.D's are useful in the superhero world too.
Villains
Darkseid: Josh Brolin
He's basically Thanos with red eyes.
Lex Luthor: James Spader
This needs no further explanation. I can't believe this hasn't happened yet.
The Joker: Tom Hiddleston
Who else? He's got the creepy smile and lanky physique.
Harley Quinn: Elizabeth Olsen
Not my strongest pick. She's the actress this role needs but not the one it deserves right now.
General Zod: Hugo Weaving
This guy is great; always delivers. Solid successor to Michael Shannon.
Harvey Dent: Bradley Cooper
Once again, an exquisite pick here. I smell an Oscar with this one.
The Riddler: Mark Ruffalo
Not sure about this one; it could either be really good or really bad. Honestly, I had the hardest time finding a spot for Marky Mark.
Posion Ivey: Cate Blanchett
Sometimes, I amaze even myself.
The Penguin: Andy Serkis
Now this... this would be something to behold and I'm all in. He could probably pull off the Joker too.
Mr. Freeze - Vin Diesel
This is a high risk, high reward pick right here but I'd gamble on it. Plus, he's bald.
Deathstroke: Frank Grillo
Dude is in like five minutes of Captain America: Civil War but he knows how to handle guns and armor. Now, just throw him an eyepatch and some swords.
Bane: Dave Bautista
He already knows the wrestling garb. Just throw him into the ring.
Catwoman: Evangeline Lilly
This is a pick you have to think about for a moment before you realize its genius.
Ra's al Ghul: Mads Mikkelson
Yep.
Hugo Strange: Ben Kingsley
If you know the character, you know this is good stuff right here.
Man-Bat: Michael Keaton
Yes, there is a character named Man-Bat and yes, he's exactly what you think he is.
Side Characters
Alfred Pennyworth: Anthony Hopkins
This a chance for the legendary actor to take a more reserved role while still spitting knowledge and ambiguous philosophy.
Jim Gordan: Don Cheadle
If someone asked me who is the War Machine to Robert Downey Jr's Batman, it would have to be the commissioner.
Jor-El: Idris Elba
Idris Elba as Jor-El is what convinced me to go with Michael B Jordan as “Supes.” Just imagine Idris Elba’s voice echoing through the Fortress of Solitude.
Lois Lane: Hayley Atwell
It's picks like these that get forgotten, yet are the reason why I believe this list is near perfect.
Mera: Natalie Portman
Hopefully, she does a better job as Chris Hemsworth's love interest than she did in the Thor movies.
Batgirl (Barbara Gordon): Letitia Wright
I know I keep addressing the quality of these choices but when it's working, it's working.
Batwoman: Gwyneth Paltrow
Honestly, I don't know too much about this character but I had to slide Gwyneth Paltrow in here. It seems fitting for Pepper Potts to be the Batwoman to Tony Stark's Batman.