According to this NASA article, the troposphere extends from about 5 miles at the poles to about 9 miles at the equator. Though the height of the troposphere is defined by the height of the tropopause as per this Aviation SE question.
I'd expect that the air pressure at the top of the troposphere would be similar at 5 miles above the poles as it would be at 9 miles above the equator.
As the altitude of an airliner increases, the angle of attack necessary to produce the same amount of lift also increases. Eventually an altitude is reached where the angle of attack necessary to produce sufficient lift is also the stall angle of attack. This pretty much defines an airplane's service ceiling. (Certainly, there are other factors, but this is a pretty big one.)
This suggests that the service ceiling would be lower at the poles than at the equator. Does this mean that an airliner flying a polar route would fly at a lower altitude than one staying in the temperate or tropical regions?