Iceberg lettuce seems to be the standard for every salad that i have eaten in Canada since arriving here last week. it is white or nearly so, unless of course it is brown around the edges for having sat around too long.
I think it is popular because you can almost freeze it in the fridge and it remains equally inedible at any temperature. That's popular with restaurants, but certainly not with me.
Salads in Canada also tend to be short on other ingredients, so if you don't like iceberg lettuce you don't find much else to chew on.
The real question is....are Canadian restaurant owners smart marketers or not?
Smart. They offer a salad that no one eats and therefore isn't worth spending good money on ingredients. It does mean they have room for more profitable alternatives.
Smart. Most people say they want to eat something healthy, but aren't prepared to pay for good ingredients for the salad.
Not smart. They are missing a great way to differentiate themselves from the dull offerings of their competitors. And these days good letttuce travels as far as bad lettuce, especially in winter in Canada.