Don’t cross a Canadian, or she’ll utter an ominous threat: ‘I’m gonna fix your wagon!’ It’s the kind of expression that you understand immediately, and it sounds like it probably stems from the days when Canadians were busy running away from bears and surviving in sub-zero temperatures without the benefit of central heating, rather than smashing each other with sticks in ice rinks and producing tins of maple syrup (maple syrup? In a tin? Whatever next?).
I’ve never heard it in Britain, where I think one would use, for example, ‘I’m gonna sort you out’, whereas in French, I would say Je vais te régler ton compte (I’m going to settle your account). Neatly enough for a translator, both expressions also contain a threat disguised as a promise of doing something positive for the offender.
Word Detective has info on the origin of that expression, which is not as old as it seems:
(…) ‘to fix someone’s wagon’ employs a perfectly innocent-sounding phrase as euphemistic slang for ‘settling a dispute for good in a very forceful manner’ (‘She said her brother would fix my wagon, which he did; right here at the corner of my mouth I’ve still got a scar where he hit me,’ Truman Capote, 1951). Oddly enough, that 1951 citation from Truman Capote’s novel ‘The Grass Harp’ is actually the earliest example found so far of the phrase in print. If the phrase is really that recent, it’s likely that the wagon in question is actually a child’s wagon (e.g., the Radio Flyer ‘little red wagon’ so popular in the 20th century US), and the phrase originated either as children’s slang or, more likely, as a sarcastic adult reference to the perceived weakness of an opponent (e.g., ‘Oh, Tommy’s decided to go back on our deal, huh? Well, I’ll just go fix little Tommy’s wagon for him.’).
Hobbes in a Radio Flyer red wagon