If memory serves me correctly the sale of ex RAAF Hornets to Canada was first mooted in the late 80s / early 90s, before the end of the cold war.
The story was that the Canadian Fleet was suffering higher attrition (or fatigue) than expected and they required additional airframes to maintain capability, with the still in production Australian F/A-18A/B being seen as the best option. The idea was the aircraft would be transferred from existing RAAF stocks with Australian production being extended and perhaps switching to C/D models to replace the aircraft supplied to Canada.