I've been using 89 octane for a long time because my mechanic told me it keeps the engine cleaner. It's very expensive here. Is there a definitive answer to this conundrum? Also, is there a difference in octane ratings between the states and Canada?
There are different octane rating systems.
Generally, the octane characteristics are the same, aside from some local areas.
Denver has lower octane because of the 18 % reduced air density.
Vancouver, for many years, had higher octane fuel available at Chevron.
Sunoco was a later player in Ontario with their higher octane fuels.
All you need is 87.
The main refiners advertise "more cleaner" as you ascend their octane ladder of fuels.
But that is pure hype in my opinion, as long as you are talking main refiners.
87 from a main refiner will be a very high quality gasoline with an excellent additive package including the cleaner component.
What is crucial to understand is that the additive package is added at the tank farm, it is NOT part of the refining process. Some additives will get added at the station, but that is a rarity ( I have personally watched a Chevron driver manually dope a load being pumped into tanks at a Chevron station and discussed the topic).
If an off brand reseller is pumping Shell, Sunoco etc gasoline, you can expect it not to have as good an additive package.
This situation is even worse re imported gasoline, is in off brand sellers buying imported fuel.
Short story, if you want the best cleaner in your gasoline as it is pumped, buy from Sunoco, Shell and Esso branded stations.
And get the least amount of ethanol in the fuel as you can.