What do Protestants think about canon laws given by the Church Fathers?

In general, Protestants don't think about the early church canon laws much at all! Protestants endorse the ecumenical creeds, and they accept the councils' judgements of heretics, but that's about the extent of our engagement with the ecumenical councils. In my four year MDiv degree I don't think we discussed the canons at all, even in the early church history subject. We discussed early church hagiography more than the canons.

Protestantism sees itself as a descendent of the early church, but its relationship to the early church is a critical one. Protestants uphold the Trinitarian theology of the early church, but they challenge many other aspects of early church theology and practice. Most Protestants would align themselves with the Antiochene school of interpretation and be highly critical of Alexandrian allegorical interpretations. So Augustine, who is highly respected in Protestantism for his theology, is evaluated critically in his exegesis when he strays too far into allegory. Some other aspects of early church thinking which are not well regarded in Protestantism include its growing Mariology, and its strange (almost creepy) focus on female virginity.

The canons themselves (they can be read here, although there are different lists on different sites) focus mostly on church polity and church discipline. Most Protestant denominations are not episcopal (ie, hierarchical with bishops), and have developed their church polities based on the Biblical passages of qualifications of elders independently from these canons (or at least they'd think of themselves as doing it independently, though some ideas could surely be traced back.) Some canons would be flatly rejected as being out of touch with general Biblical teaching and wisdom:

10: All those of the faithful that enter into the holy church of God, and hear the sacred Scriptures, but do not stay during prayer and the holy communion, must be suspended, as causing disorder in the church.

27: Of those who come into the clergy unmarried, we permit only the readers and singers, if they have a mind, to marry afterward.

50: If any bishop or presbyter does not perform the three immersions of the one admission, but one immersion, which is given into the death of Christ, let him be deprived; for the Lord did not say, “Baptize into my death,” but, “Go ye and make disciples of all nations, baptizing them into the name of the Father, and of the Son, and of the Holy Ghost.” Do ye, therefore, O bishops, baptize thrice into one Father, and Son, and Holy Ghost, according to the will of Christ, and our constitution by the Spirit.

54: If any one of the clergy be taken eating in a tavern, let him be suspended, excepting when he is forced to bait at an inn upon the road.

69: If any bishop, or presbyter, or deacon, or reader, or singer, does not fast the fast of forty days, or the fourth day of the week, and the day of the Preparation, let him be deprived, except he be hindered by weakness of body. But if he be one of the laity, let him be suspended

But some canons are seen the practices of other denominations, such as this one by the Brethren, though they would likely say they are following Biblical examples rather than the canon:

34: Do not ye receive any stranger, whether bishop, or presbyter, or deacon, without commendatory letters; and when such are offered, let them be examined. And if they be preachers of piety, let them be received; but if not, supply their wants, but do not receive them to communion: for many things are done by surprise.

Now the exception are the Anglicans, whose polity is inherited from the Catholic Church. As such, they have maintained the relevance and authority of many of the canons, including such ones as bankruptcy being cause for immediate disqualification of the clergy. (I am not sure whether the Lutheran churches, who also have episcopal polities, have kept the canons as well.) Many of the canons concerning bishops and clergy still rule the Anglican churches, although their formal authority comes from being included in the current Anglican church canon law, not their ancient pedigree.

Some ancient canons have been seen to be directly relevant to current issues, such as when conservative GAFCON bishops gathered in the US in 2017 to ordain Andy Lines as a missionary bishop to England. In response Archbishop of Canterbury Justin Welby, and others, said that this action contravened these canons from the Council of Nicaea:

6: Let the ancient customs in Egypt, Libya and Pentapolis prevail, that the Bishop of Alexandria have jurisdiction in all these, since the like is customary for the Bishop of Rome also. Likewise in Antioch and the other provinces, let the Churches retain their privileges. And this is to be universally understood, that if any one be made bishop without the consent of the Metropolitan, the great Synod has declared that such a man ought not to be a bishop. If, however, two or three bishops shall from natural love of contradiction, oppose the common suffrage of the rest, it being reasonable and in accordance with the ecclesiastical law, then let the choice of the majority prevail.

15: On account of the great disturbance and discords that occur, it is decreed that the custom prevailing in certain places contrary to the Canon, must wholly be done away; so that neither bishop, presbyter, nor deacon shall pass from city to city. And if any one, after this decree of the holy and great Synod, shall attempt any such thing, or continue in any such course, his proceedings shall be utterly void, and he shall be restored to the Church for which he was ordained bishop or presbyter.

16: Neither presbyters, nor deacons, nor any others enrolled among the clergy, who, not having the fear of God before their eyes, nor regarding the ecclesiastical Canon, shall recklessly remove from their own church, ought by any means to be received by another church; but every constraint should be applied to restore them to their own parishes; and, if they will not go, they must be excommunicated. And if anyone shall dare surreptitiously to carry off and in his own Church ordain a man belonging to another, without the consent of his own proper bishop, from whom although he was enrolled in the clergy list he has seceded, let the ordination be void.

Each Anglican province is formally independent, and sometimes ordinations are recognised by those who decide to recognise them rather than it being a matter of rules. Even so, these early church canons are still recognised in the Anglican churches, and appeals can be made to them, even if not all of them are legally binding. Those in favour of the missionary bishops do not completely disregard these canons but argue that they are not directly applicable to the current situation, such as this response by Australian Rob Smith.

And one final sad note, it is possible that canons such as these were part of how prior generations of church leaders justified themselves for not seriously investigating allegations of clergy sexual abuse.

75: Do not ye receive an heretic in a testimony against a bishop; nor a Christian if he be single. For the law says, “In the mouth of two or three witnesses every word shall be established.”