A phrase used by Canadians to indicate that the person being addressed is in deep trouble. Usually (but not always) it is the person uttering the phrase who is offering trouble to the one being addressed.
1) Joe: "Hey, I broke your favourite autographed hockey stick; sorry..."
Wayne: "Oh, you're toast, eh!"
2) Wayne (at the bar): "Damn, is it 3am already? I promised my wife I'd be back by 11!"
Joe: "Oh, you're toast!"
My dad had the nerve to tell me that If I didn’t do some shit related to a car that I didn’t know jack-shit about, then he would just say to me “you’re toast”