Here are some Azumanga Daioh crossovers you may have seen before:
http://koti.phnet.fi/otaku/azucross/azucross.html
Looking at these, I had my own idea for a crossover: AZULIBRIUM!
Sakaki = Christian Bale's character (Preston)
Kagura = Taye Diggs' character (Brandt)
Kaorin = Emily Watson's character
Chiyodad = Father
Nyamo = Sean Bean's character
Yukari = DuPont
Kimura = Jurgen
Chiyo = Preston's daughter
[spoiler=My reasoning]Sakaki, in my opinion is the best choice for Bale's character. She is cool, but has a tender emotional side. This is almost comprable to Bale's initially cold, emotionless character who ends up becoming sensitive to the things around him. Plus they are both exceptionally fit.
Kagura is the best choice for the Taye Diggs character. The Sakaki/Kagura relationship is almost exactly like the Bale/Diggs one, in which both are in a civil, but competetive, bond. Kagura declares herself Sakaki's rival, but they are friends most of the time. And Taye Diggs acts politely to Bale, but more than once says, "One of these days, I'm going to make my career with you" (or something to that effect). Also Diggs' abilities are a close match for those of Bale, just like Kagura is a close match (at least athletically) to Sakaki. But both were outwitted by their rival (Sakaki scored much higher on the exam than Kagura, and Bale pulled the old switcheroo on Diggs).
Kagura is clueless about Sakaki's love for cats as Diggs is clueless about Bale's newfound fondness for dogs.
Only Chiyodad could be Father. Both are ubiquitous and speak with commanding voices. Plus, Chiyodad as father is just plain hillarious. (Not to mention he claims to be someone's father).
Kaorin as Emily Watson's character doesn't work that well, but I just thought somehow she would fill the role well. Emily Watson is the one who first notices (and encourages) Bale's awakened emotions. That doesn't quite match Kaorin's puppy-love for Sakaki, but I'm sure Kaorin wouldn't mind talking "seductively" to Sakaki.
I only picked Nyamo for Sean Bean's character because she's older than Sakaki (as Bean is older than Bale). If age was the only criterion, Yukari could also have been picked for this role. But I wanted her for DuPont, because DuPont is evil and selfish and hypocritical and so is Yukari (at times).
And why Kimura as Jurgen (the leader of the Underground)? There isn't anything particularly alike about them. However, they both have an unkempt aura about them. I mean, look at Kimura's hair.
Finally, some changes. The "infamous dog scene" will have to be replaced with cats. (Just imagine Sakaki watching dozens of cats getting shotgunned to death). Also, since the main character's sex is flipped, her spouse is now a man. Since Kimura is the only human male in AD (and TOTALLY incompatible with Sakaki), I elect Mr. Smarty Pants to be Sakaki's husband. (It's not as great as it sounds, MSP. Emotions and love are banned, and your character gets to be summary incinerated for those offenses). [/spoiler]