In Ontario this is a bird of village shade trees or by rural roadsides, not a dweller in forest tree tops like the Red-eyed Vireo. In winter they go south to Central America.
It is a small vireo with no wing bars. The pale line over its eye is not bordered above and below with dark lines as in the Red-eyed and Philadelphia Vireos.
It is best identifies by its song which is a long warble, much like the song of a Purple Finch but always ending with a question (a rising pitch).