Our highest mileage car that saw 99% highway everyday had oil changed at the longer of the two intervals(12000km/7500miles) for the first 300 and something thousand km. Once it got around 400 and was used only in the city I changed it more often at 6000km/3700miles like the rest of the ones in the fleet. Basically if you live in Canada and use the car like a car you need to follow the severe schedule according to the manual.
If it ever warms up here I'm gonna pour some thicker oil in my personal 2014 Mirage when I change it(or next time it's low) to see if it'll shut up the rattling engine. I've got some 5w40 and a bunch of gear oil to try. I've basically got no engine warranty as I have no proof of previous service history so I'll keep it going til it starts using more oil than gas or get louder than the radio.