Even John Calvin Himself seemed to "waffle" on the issue of limited atonement, as have read Calvinist scholars who used him to deny/support it
I think the worst that could be said was that he was not
explicit on the topic, unlike the other four so-called points of Calvinism. So there are plenty of statements in the
Institutes that imply God's universal love for mankind or intent to offer salvation to all men.
However, Calvin believed in penal substitutionary atonement, with Christ's death not merely making salvation possible, but making it effective. In his commentary on 1 John 2:2, he writes:
Here a question may be raised, how have the sins of the whole world been expiated? I pass by the dotages of the fanatics, who under this pretense extend salvation to all the reprobate, and therefore to Satan himself. Such a monstrous thing deserves no refutation.
Propitiation, in other words, can't be universal. Self-evidently, the sins of all people indiscriminately have not been expiated. Calvin was aware that some were of the opinion that the Atonement was "sufficient for all, efficient for the elect"; however,
[t]hough then I allow that what has been said is true, yet I deny that it is suitable to this passage; for the design of John was no other than to make this benefit common to the whole Church. Then under the word all or whole, he does not include the reprobate, but designates those who should believe as well as those who were then scattered through various parts of the world. (
Source)
Incidentally, this parallels something John records in his Gospel that the high priest said: "he prophesied that Jesus would die for the nation, and not for the nation only, but also to gather into one the children of God who are scattered abroad" (John 11:51-52). The wording parallels that of 1 John 2:2, perhaps giving us some insight into what John meant when he said Christ is the propitiation for the "whole world": not just Jews only, but Jews and Gentiles together. The "whole Church" is scattered throughout the whole world.
Calvin's theology was strongly covenantal, and the covenants into which God entered with his people were particular, not universal or indefinite.
So while Calvin may have been indistinct on that particular topic, the overall tone of his theology would make a stronger
indirect case for a definite atonement than a general one.