14A in US terms is usually rated R alot of the times.
This is what 14A is defined as: Suitable for people 14 years of age or older. Those that are under 14 should view with an adult. May contain violence,coarse language and/or sexually suggestive scenes.
Because up in Canada,it seems that alot of the times when rated R movies come out that are rated R there we Canadians end up rating it 14A. Once a blue moon the rated R movie will become 18A or will remain rated R in Canada. It is also possible for a PG-13 movie to be rated 14A too,that's what happened with The Dark Knight. I'm basically basing most of this information based on the fact that I work at a movie theater called Cineplex Odeon.
18A: Suitable for people 18 years of age or older. Persons under 18 should view with an adult. Parents strongly cautioned. Will likely contain explicit violence, frequent coarse language, sexual activity and/or horror.