Actually a prochronism, Lisa's ancestor is shown living in a log cabin in mid-1800s Canada, but the Canadian flag shown outside is the red and white maple leaf design which wasn't invented until 1964 and didn't become official until 1965, a time difference of over 100 years.
In 1860 Canada was still a British colony. It didn't become an independent country until 1867. And the Canadian maple leaf flag wasn't adopted until 1965.
Eliza Simpson's diary says that she attended a grand ball on April 14, 1860. At the ball, an orchestra is playing An der schönen blauen Donau (the Blue Danube Waltz), by Johann Strauss II, which wasn't written until 1866.
A double barreled shotgun was shown in an 1860 flashback but it wasn't invented until 1875.
Milhouse's ancestor wrote in his diary that he was sitting under a "sarsaparilla tree". Sarsaparilla is actually a climbing vine.