Generally, the alleged discontinuities are not considered solely on the basis of Calvin’s thought and the WCF, but compare first Calvin and Dordt and then the oft-discussed comparisons between Dordt and the WCF. As to the former, it has often been asserted that the formulation at Dordt was more Bezan than Calvinian, particularly with regard to the doctrine of the atonement. R. T. Kendall’s (Calvin and English Calvinism to 1649) is perhaps the loudest voice making that case. Paul Helm notably (and directly) rebutted Kendall (Calvin and the Calvinists). Richard Muller, Roger Nicole, and Robert Godfrey are also helpful here.
Largely, the issue arises because Calvin’s focus was, quite frankly, more pastoral than systematic, as he was concerned with re-educating the people who had been immersed in Roman Catholicism. The task of more precisely defining the doctrines fell to his successors as the need to defend their theology became more necessary. Still, Beza himself said:
“I confess that I am one of those the Lord has educated in the true and holy doctrine of his Gospel by his faithful servant John Calvin. I will certainly never be ashamed to call myself his disciple and one of many thousands of men that he has won to Christ.” (Tractationum Theologicarum, i.422)
The whole “Calvin against the Calvinists” idea with regard to Calvin vis-à-vis Dordt would seem to be overinflated, in my opinion.