The song that Christy Carlson Romano sings is a cover of the song Doris Day sang in Teacher's Pet (1958), but the 1958 film has no other connection to this film or the Teacher's Pet (2000) cartoon show.
Nathan Lane and Jerry Stiller's first collaboration in 2004. Their second is in The Lion King 1½ (2004), one month later. Coincidentally, both films were released by Disney.
A deleted scene shows Pretty Boy and Mr. Jolly wondering how they're going to get home without Mary Lou noticing. Spot once more adopts his Scott identity so that he can get home with the Helpermans while the other pets cling to the back of the family's RV.
The hotel Scott stays at in the third act is called the Hotel Louis Versaille; the letters that flicker spell "Loser".