To start, Simon Kinberg is supposed to be writing it, and given his writing credits, I'd give it a 50/50 shot at being adequately written. I mean, I wasn't a fan of the Sherlock Holmes with Robert Downey Jr, but other people liked it, so I'll give that a pass. However, I didn't really like his handling of established characters in X-Men: The Last Stand, so that counts against my hopes. I also have zero faith in Fox in general, so that's a knock against this too (for me at least). But, rather than go into anymore details about my lack of hope for the film (the last WotC film was Dungeons & Dragons remember), I'm going to give you my thoughts on what would be the best cast for the film. Might as well give this movie a shot, right? Now, I doubt this thing will be given oodles of money, so I'm picking from a "discount actor list" of sorts. Also, I'm about to sound really pretentious, so apologies in advance.
Urza: Jeremy Irons
In the vain hope that the classic planeswalkers will make an appearance, I really hope Jeremy Irons is on the shortlist to play Urza. I don't care what people say, I love his acting. Yes, he was corny and over-the-top in Dungeons & Dragons, but he was amazing in The Borgias and The Lion King. He brings all of the necessary class and pomp required of the greatest planeswalker of all time.
Karn: Vincent D'Onofrio
Since the more likely scenario is a newer storyline, Karn would be well-served by Vincent D'Onofrio. This man can do everything and that dedication is what a complex role like Karn would need to bring his story to the screen. His voice is great, his acting is great, everything about what Vincent brings to the screen is what a character like Karn needs.
Chandra: Paget Brewster
I really think Paget Brewster is a great actress that seems to thrive in nerdy roles (Batman: The Dark Knight Returns, Dan Vs., Harvey Birdman, etc) and this would be a perfect movie role for someone like that. I've seen (and heard) a lot of her work, and I just see her pulling off a good Chandra.
Teferi: Dwayne Johnson
Was there any other choice? For those who remember, Teferi was kind of a prankster as a child and I think that Dwayne could pull it off. He's shown his acting chops and I think that Teferi would be a good role for him. He's fun, he's playful, he's the best guy to play Teferi. Oh, and for those saying "Teferi isn't muscular!": bleh. I personally think that jumping around space and time would give you some guns.
Elspeth: Samantha Morton
I'll admit that I didn't know who this was until I started this list, but I know her work and I like it. I found a clip of Samantha in Minority Report and I instantly thought that she could make a good Elspeth. Seriously, look at that movie and tell me you couldn't see her stabbing Tom Cruise with a giant spear.
Jace: Michael Weatherly
Take a deep breath and hang on to your flame comments until after you read my reasons why I think Michael Weatherly would make a good Jace. Jace is a cocky, over-confident jackass who can't do everything he thinks he can, right? Well, that sounds a lot like his character on NCIS, doesn't it? Jace also has to break off important relationships in order to protect the other person, but still fights himself over the decision, just like Logan in Dark Angel, another one of his characters. What I'm saying is, Michael Weatherly has essentially played Jace most of his career, just in small parts. Okay, you can commence the fireworks now.
Well, that's who I think should play whom in the Magic movie. And, if they don't actually care about the movie at all, here's who I think they should pick to try and get "so-bad-it's-good" status.
Urza: Al Pacino
Karn: Vince Vaughn
Chandra: Kristen Stewart
Teferi: Bokeem Woodbine
Elspeth: Adam Sandler in a wig
Jace: Christian Slater