The U.S. IGA web site says they have a "fraternal relationship" with the Canadian IGA. I don't know if that means they get together at the supermarket reunions and punch each other in the arm, or if they're eyeing each other with suspicion from across the border, or what.
Since it is, as the name implies, an association of independent grocers, each IGA store is unique, and may be anything from a gigantic modern supermarket in the suburbs to an old brick general store on Main Street.
Some of their stores used to go by the moniker "IGA Foodliner," spelled out on the facade with each letter painted in red on its own individual white rectangle. Whether that was supposed to mean that the stores were the size of an ocean liner, or that the interiors were lined with food, no one can say.
I have in my collection a radio jingle for IGA from the early 1970s:
We invite you
To your neighborhood IGA
It's easy shopping, friendly IGA
Where else but IGA?
That pretty much says it all.