Director Rob Minkoff chose Ty Burrell for Mr. Peabody because "his voice embodied all the different aspects of the character today - not just the intellect and the suave personality, but the underlying warmth as well."
Robert Downey Jr., Kelsey Grammer, and Geoffrey Rush were considered for the role of Mr. Peabody. Downey was originally cast, but had to drop out due to scheduling conflicts, similar to how he and his Tropic Thunder (2008) co-star Ben Stiller lost the titular role of Megamind (2010) to Will Ferrell.
Marie Antoinette's obsession with "cake" in the film is due to the rumor that when the peasants complained of their lack of bread (and food for that matter), she said "let them eat *brioche*." This word means expensive bread, but was later mistranslated as "cake." However, there is no real evidence that Marie uttered such words, which have also been attributed to another French queen about one hundred years earlier. The reason the peasants revolted wasn't due to such a quote as depicted in the movie, rather she and King Louis XVI were taken from the Versailles palace to Paris by a revolt of angry peasant women after they discovered the royals had been hoarding grains from the rest of the people. This is also debatable, as the specifics of this affair are not really known, regardless, their house arrest was due to the peasant revolt during France's early Revolution. Peabody and Sherman previously visited these historical figures in Louis the XVI (1961).
Sherman sleeps with a stuffed animal of Horse from The Dudley Do-Right Show (1969), another division of the Bullwinkleverse.
Mona Lisa complains about sitting around on her "abbondanza". This word means "abundance" in Italian. (It should be noted that the painting is called "The Mona Lisa". "Mona Lisa" is not the name of the woman in the painting.)