Not to play compare/contrast forever, but in real life, Travers resembled the late Washington journalist Helen Thomas more than Emma Thompson (who looks a lot like my mother in this particular get-up, as it happens), and Disney didn't exactly talk with the "Tom Hanks Generic Southern Accent." Still, Hanks' unofficial role as America's most beloved non-threatening celebrity makes him a perfect fit spiritually; in that capacity, he's a far better choice than fan-pick Ryan Gosling, subject of popular photoshopping into fake Disney biopic posters. Travers isn't as well-known to us as the ubiquitous Walter Elias, but Thompson certainly conjures up all the OCD Englishness we'd imagine she must have had, complete with meds for it (the end credits, featuring actual Travers audio, seem to bear this out).
Howard, yes. Gosling, not so much
More controversial in the casting department is Colin Farrell, who plays Travers' father in flashbacks to her childhood in Australia. Those who've come to see a comedy about the Hollywood development process are more likely to resent the constant switches in time, but Farrell, who presumably knows a thing or two about being a lovable boozer from experience, does decently with a challenging part - he's an irresponsible drunk who fails his family on a professional/breadwinner level, yet his alcohol-fueled fantasies inspire him to create magical playtimes for his children. While director John Lee Hancock (The Blind Side) arguably lingers too long on Papa's story - the best bit is when he cuts back and forth in time to have Farrell suddenly sing a Sherman brothers song from the '60s present that fits the character in his moment - he is to be credited for giving us a more dimensional drunkard than other movies might have.
If you cannot relate to any of this, the film will not work - as history it's dubious, and as drama, it's predictable; hell, we all know how it has to end, because it's not like Mary Poppins didn't get made. It's in the character and performance details that it all comes to life - ironically, the dramatic medicine that helps the copious spoons full of sugar to go down.
Saving Mr. Banks is currently in limited release, and opens wide Friday.