Leo McCarey was supposed to direct the film, but shortly before the filming began he was injured in an automobile accident, and had to hand over the direction to Garson Kanin. Actress Gail Patrick has stated that the severity of McCarey's injuries had an effect on the film's cast, and they found it very difficult to enter into the spirit of the comedy with the serious hospital bulletins they were hearing.
The hotel in the mountains is clearly meant to be the AhWahnee Hotel in Yosemite National Park. Its kitchen has won prizes and they serve an elaborate Christmas dinner, but it's expensive and you need to book about a year in advance.
Cary Grant wears a leopard print smoking jacket throughout much of the last third of the film. Two years earlier, he had co-starred in the immensely popular Bringing Up Baby (1938) in which the titular character is a leopard.
It is odd that when Ellen shows up, she is dropped off by someone driving a delivery truck. No one from customs or the shipping company has helped her get home, nor has she sent a message by the wireless, which was practically universal in use to send telegrams. It is also odd that she says she hasn't had a hot shower or bath "for years" when hot water showers are common (necessary and easily accomplished on a ship with boilers). This can't be her first shower, she must have had one on the rescue boat.
In addition to the 1963 Doris Day/James Garner remake Move Over, Darling, this film's script also served as the basis for Marilyn Monroe's final, unfinished project, Something's Got to Give. That version featured Dean Martin in the Cary Grant role, and Cyd Charisse as the second wife. Some of the sets built for that version were "re-purposed" for the Day/Garner film, after production on the Monroe/Martin movie was shut down due to Marilyn's chronic tardiness, and eventually abandoned when Monroe died in August of 1962.