I love this contest. I can think of a few offhand that I just absolutely adore.

My favourite Canadianism is, by far, "You hoser." It's a playfully derogatory term to call someone a loser. In the late 19th, early 20th century ice hockey was played outdoors and there were no machines to clean the ice. The losing team was required to scrape and "hose" down the ice after the game, hence the term "hoser".

Some of my other favourites:

"Three (or four) sheets to the wind" for "falling over or passed out drunk."
"Four flusher" for "a$$h**"
"Sht or get off the pot" for "good god, make a decision."

Yes, I'm juvenile.