I would say the complications run much deeper than the R2K contingent of the URCNA. Continued Schilderian (CanRC) animus against Kuyperianism (URCNA) is more fundamental to the problem. In some ways the URC doubled down on Kuyper after the CRC split (especially with respect to local autonomy) and many in the CanRC still remember how Schilder was treated by the Kuyperians in both the CRC and the PRC. Beyond the historical/emotional divide, Schilderian theology has made the CanRC receptive to Federal Vision heresies which has been a huge sticking point, obviously. Schilderianism is not the same as FV, but there are similarities and those similarities has led to much sympathy for it. My wife's previous CanRC pastor was one whose bookshelves were littered with Doug Wilson and James Jordan and saw no reason for concern in them. Other CanRC pastors and elders openly questioned and denied the URC Synod's statements on Federal Vision. I think things may have improved somewhat in the last few years, but it seems to me that the CanRC still has some things to work out there. R2K may be an issue too in that it's more compatible with the Kuyperianism of the URC than the Schilderianism of the CanRC, but from my view that was a much smaller point of contention. If "Crocodile" Wes Bredenhof is still around perhaps he could add.
You are probably more well versed on this than I am. I know there is a good bit on contention over Schilder on the URC side (I cannot comment on the Canref on this)especially since a good chunk of his work remains untranslated. I know from where I am in the URC there is the opinion that the R2K guys overshoot on the idea that the Canref is a FV haven. From where I am it seems that the westcoast URC is a fairly different animal than the Midwest, Canadian and Eastcoast URCs and I have seen more affiliation with Canref guys where I am at. I am also an outsider to all the Dutchy squabbles that take place an are even harder to explain.
And the other part of the question, why would have joined these RCA churches the PCA rather than URCNA? URCNA is Dutch origin, PCA is Southern Presbyterian origin. Why these churches felt that the PCA would be better option? They hade to adopt WCF besides TFU.
Again weird Dutchness, from what I understand the RCA and CRC were very different in the practical expressions of their theology to the point that the conservative RCAs were much closer to the more american PCA than the somewhat ethnically cloistered URCs