California Doubling: A movie about events that took place in Winnipeg, written by a Winnipeg writer, starring a Winnipeg actress... was set in Chicago and filmed primarily in Toronto.
The Danza: For some reason, Toula's name was changed to Nia for the TV series, even though everything else about the film (barring only John Corbett's replacement by Steven Eckholdt) remained the same for the series. The sequel reversed this change.
Michael Constantine who plays Gus was born Gus Efstratiou.
Dawson Casting: Vardalos was 39 when the movie was released, but Toula is 30.
Executive Meddling: A rare positive example, as many of the best things about the film turned out to be studio-mandated changes that Nia Vardalos fought tooth and nail. Her entire career since the film is a testament to how badly it could have gone.
Nia Vardalos is a Greek-Canadian playing a Greek-American. (though she has become a naturalized US citizen since then)
Lainie Kazan is Russian Jewish on her father's side and Turkish Jewish on her mother's side.
Michael Constantine was born in the United States to Greek immigrant parents.
Andrea Martin is an Armenian-American; the scene where Rodney & Harriet try to recall the ethnicity of Rodney's secretary, which turns out to be Armenian, may be a reference to this.
Gia Carides is Greek-Australian (she was in Strictly Ballroom and is married to Anthony LaPaglia)
Joey Fatone is Italian-American.
One-Hit Wonder: This was Nia Vardalos's only project to have any sort of success. Her subsequent projects have mostly failed critically and financially. After ten years of failed projects she managed to get a sequel to this film off the ground, which actually did do reasonably well at the box-office, but further reinforced the perception that her only major successes have been from this series (and even then it's tempered by how badly My Big Fat Greek Life bombed).
The Other Darrin: Nia Vardalos and most of Toula's family came along for the TV series, but John Corbett had to be recast.
Real-Life Relative: Ian Gomez, Nia's real life husband who was directly involved with the inspiration for the movie, plays a friend of the groom.
Leads to an Actor Allusion, as Ian Gomez's character flatly states that there's no way that a gorgeous woman like Toula would even look at a guy like him.
Sequel Gap: The second film was released 14 years after the original.
Sleeper Hit: Turned a $5 million budget and a limited release into a $241 million domestic tally, thanks in part to such great word-of-mouth that the movie stayed in the top 10 weekly box office for over three months, gradually getting a wider release with each passing week due to its success. Some of the films it outgrossed on its shoestring budget: Austin Powers in Goldmember, Men in Black II, and Die Another Day.
What Could Have Been: Tom Hanks helped produce the film but found some difficulty getting it made. The studios liked the idea but wanted to cut the "Big," "Fat," and "Greek" part out and cast someone like Jennifer Lopez in the main role (as a thirty year old woman who has trouble dating, yeah). That's the reason it went indie and turned out the way it did.
For all of Gus's bluster about Greek words, Portokalos isn't even a native Greek word! It's derived from the name Portugal which is the country that introduced oranges to Greece.