pole horse vs poler

pole horse and poler both are nouns.

Word	Noun	Adjective	Verb	Adverb
pole horse	Yes	No	No	No
poler	Yes	No	No	No

As nouns, pole horse and poler are synonyms defined as:

pole horse and poler: a draft horse harnessed alongside the shaft or pole of a vehicle

pole horse (noun)	poler (noun)
a draft horse harnessed alongside the shaft or pole of a vehicle	a draft horse harnessed alongside the shaft or pole of a vehicle
the horse having a starting position next to the inside rail in a harness race