In ‘Justin Against Marcion’ (Fortress, 2017) Andrew Hayes notes, “The relationship of Marcion and the canon is not something Justin (Marcion’s contemporary) discusses.” In Justin’s First Apology, I.26, (155 CE) he says Marcion is “teaching his disciples to believe in some other god greater than the Creator. And he, by the aid of devils has caused many of every nation to speak blasphemies, and to deny that God is the maker of the universe, and to assert that some other, being greater than He, has done greater works”. Irenaeus, in ‘Against Heresies’ (c.180 CE, 20 years after Marcion’s death) at 1.27, says, “He mutilated the Gospel According to Luke.” (And Irenaeus was also the first person to identify the four gospels as Matthew, Mark, Luke and John). Irenaeus further says, “he dismembered the epistles of Paul, removing all that is said by the apostle respecting that God who made the world, to the effect that he is the father of our Lord Jesus Christ.” At Earlychristianwritings.com a reconstructed Marcionite gospel can be found, using quotations from Tertullian (b.160, the year Marcion died) and Epiphanius (b.310). His “canon” was unmentioned while he was alive.
See NT Review. Adolf von Harnack, Marcion: The Gospel of the Alien God here: https://podtail.com/en/podcast/new-testament-review/22-adolf-von-harnack-marcion-the-gospel-of-the-ali/