G'wan, b'y

Atlantic-Canadian slang phrase used very commonly in Nova Scotia and Newfoundland, translates word-for-word as: "go on, boy!" and is commonly used as a term of disbelief, as in "No, really?".
East-Coast Canadians also spell it as "Gowan b'y" in text form.

"Dere gon' be a flood!"
"Ah g'wan, b'y"