Most companies has limited options on Wednesday morning at YYZ.
If you want to access the aisle, simply book with National, they have way better collections than Hertz.
If you need more premium car, book with either Enterprise or National since National/Alamo/Enterprise share the same fleet at YYZ.
It's always YMMV in terms of upgrade at this location, but I've found National agents are bit more accommodating. During week days, there might be some V8 or convertible Mustang available for upgrade.

If you need Tesla, book with Hertz. Other than that, I would avoid to rent with Hertz at YYZ, PC means nothing (very limited choices and high mileage cars), but you can always book a back up reservation with them.