I've actually devoted two posts in my blog (please pray that part 3 will see the light of day :)) specifically on this issue.
"The Pope and God are the same, so he has all power in Heaven and earth." Pope Pius V, quoted in Barclay, Chapter XXVII, p. 218, "Cities Petrus Bertanous".
This seems to be another case of 'hiding behind the curtain of obscurity' as we are merely given the author's surname of Barclay, with no reference to a book title.
As for the identity of this mysterious 'Petrus Bertanous', this author personally tends to believe that this refers to a certain 16th-century Dominican named Petrus Bertanus Fanensis (aka Pietro Bertano; November 4, 1501, Nonantola-March 8, 1558, Rome), who once served as bishop (later cardinal) of Fano in Italy -- the present-day diocese of Fano-Fossombrone-Cagli-Pergola -- and who, among with other Dominicans, was apparently one of the leading prelates at the council of Trent and was an orator and advocate at that same council.
During the papacy of Pope Julius III (who reconvened the second period of the Tridentine council in 1551 after Pope Paul III died in November 10th 1549 at the behest of Emperor Charles V/Charles I of Spain), who entered into a league against the duke of Parma and Henry II of France (1547–59), the Emperor's party requested that Julius admit eight people into the college of Cardinals. Four of them are to be named immediately and the other four are to be reserved in petto until conditions became more favorable; one of those whom they requested to be named immediately is Bertano, who was a member of the imperial party. Eventually he, along with thirteen others, were made cardinals on November 20, 1551, as a sign of reassurance to Charles (especially considering that all fourteen were favorable towards him).
While at first glance this connection may seem plausible (considering that both Pius V and Bertano were both Dominicans), we have to consider the following:
1.) This quote is attributed to Pope Pius V by "Bertanous" (sic). However, Michele Ghislieri O.P. only ascended to the Chair of Peter in January 7, 1566, about eight years after Pietro Bertano died. How could someone who is not then a pope make a statement about the papacy, much less someone who was dead at the time Ghislieri became pope?
2.) Considering that at the time Fra Pietro is still alive, Fra Michele still does not have the power of pronouncing ex cathedra statements - as he was not pope yet - are there chances that his statement (let's suppose for a moment that his "words" are true and are either not a misquote, mistranslation, or just flat-out made up) are actually reflective of official Church teaching?
3.) Are there any more reliable and independent sources for this quote, if any, aside from this rather obscure (and badly-titled) one?
Some sources for this 'quote' add the following phrase: "Cardinal Cusa (i.e. Nicholas of Kues)* supports this statement.*" Now, are there any contents from Cardinal Nicholas' work which support this quote? Here is a chronological listing of Nicholas of Cusa's works. If anyone can point out a paragraph or a sentence in his works (if anyone has them) which says very much the same thing as above (preferably the original Latin included), I'll be glad to put that up.