Can·a·di·an·ism: a word, expression, or other language feature that is characteristically Canadian.
One of the most popular Canadianisms is the word “eh.”
In linguistics, eh is referred to as an invariant tag.
A tag is a word, sound or short phrase added after a declarative statement which changes that statement into a question.
In the sentence, “It’s a nice day, isn’t it?”, isn’t it is used as a tag which changes the statement, “It’s a nice day” into a question. Similarly, in the sentence, “It’s a nice day, eh?”, eh is the interrogative tag.
Invariant refers to the fact that the tag is not affected by the subject or tense.
It’s a nice day, isn’t it?
It was a nice day, wasn’t it?
vs
It’s a nice day, eh?
It was a nice day, eh?
The Modern English eh derives from Middle English interjections such as ey and ei and a. It had traditionally been used as an interjectional interrogative particle (aka, a verbal question mark) before appearing in written form in 18th century Europe. Literary works imported with settlers to Canada, from Ireland and Scotland, likely greatly influenced the evolution of Canadian English.