John Sununu's office has just released a pretty clear answer on cloture for the immigration bill:
RE: Future cloture vote in immigration. On this bill, no. On this bill with any amendments proposed by bipartisan group, no.
Senator Sununu opposes the immigration bill - voted against it last year, and has voted twice against cloture on immigration this year – both on June 7.
So I'll keep Sununu as Very Unlikely to Switch. But this does confirm it.