I'd say that once a car is warmed up (everything; all fluids, greases, tires, etc) then wear is fairly minimal to nonexistent at steady speeds.
But stop-and-go, extended idle and the rest put a real strain on oil in high ambient temperatures.
And, no, Canada doesn't get all that hot, not compared to the American Southwest. Try Dallas-Ft Worth where the overnight ambient low doesn't get below 90F for several months. Or below 100F before midnight. And add in the humidity produced by this region and it feels hotter than even Phoenix sometimes. Florida at least gets double the rain and ocean breezes to amieliorate conditions.
Those conditions are murderous on cooling systems, and, as oil has to cool the bottom-end of the motor (40% of required engine cooling), todays cars -- and some SUVs -- have a real problem in coping after only a few years of operation due to weight/size and packaging considerations.
Add to that the trouble the A/C condensor is having in transfering heat -- much of it past the radiator -- and one can see that engine oil maintenance is crucial.
Synthetic oil has been mandatory, in my estimation, for the longest engine life in like-new condition. Although there are UOA's of dino with excellent numbers (and I may well change brand or viscosity of my current choice), synthetic is worth a little peace of mind, IMO.
Yes, summer conditions in this part of the country make a difference per the original question.