Going by these past performances, should Pop give Blair regular minutes in this series? If so, what type of role should Pop give Blair? If not, are you confident in Boris Diaw and Matt Bonner being able to have similar success against Millsap?
No. Not to start, at least. If things aren't going according to plan and/or Diaw is playing atrocious, then re-assess things at that time. But theoretically speaking, Diaw is an idea Millsap defender. Millsap thrives on generally having a strength or quickness advantage. Unfortunately for him, Diaw possesses both of those attributes as well.

If it comes to Blair replacing him, then Blair should start. There's a comfort level and level of familiarity there and it would keep the bench/rotation intact.

I'm confident in Diaw and Bonner doing at least an adequate job on Millsap, but I don't think that matters that much in the grand scheme of things though. The Jazz are going to have to have damn near everything break just right just to have a fighting chance at pulling this off. Having one of their two best players playing well is something that should be more expected than unexpected.