Plot hole: Once the gang have arrived in Canada, Daphne is scared stiff of getting caught outside the USA. Marty explains they will just "smuggle" her back and Frasier and Niles are outraged at such deception. But to get into Canada, all of them would have had to declare their residence, birthplace, and reason for coming in. To get Daphne in in the first place, they must have lied. She would have had to show her passport as an alien. The Americans would have been allowed in without their passports, per diplomatic agreements. So the outrage of the boys makes no sense.
Continuity mistake: While Frasier is driving, Marty has the map on his lap. During this scene the map changes appearance and size from shot to shot even though Marty never opens it up.
Chosen answer: The turkey's stuffing.