Oh boy. Lots of questions, and a variety of possible answers. Before I say anything, I need to know what you mean by "willing to offer some protection". Do you mean cover the roots with mulch... or bring the planter into the house or garage for the winter with additional supplemental light? Big difference.

not willing to dig up plants and bring them in every year but I certainly can mulch and am also willing to tent the area with 5mm plastic to create a temporary greenhouse in the winter.

Okay. I would suggest if you just wanted one plant: P. caerulea, though the fruit is not tasty, (nor will you likely see any with only one plant). Another option would be P. incarnata, which has decent tasting fruit, but it appears that many/most/all? varieties of this require another Passiflora for fruit production. Also, in your climate you have one strike against you. It is not the cold, but the WET cold. You would need to somehow protect the roots from any rain during any period where it gets exceedingly cold, (all winter).

I hope this helps a bit. Shout if you have any more questions.

well, where I am it fortunately doesn't get 'exceedingly cold' ALL winter, most of the winter stays in the 40s, there are only 2-3 weeks that we tend to drop below freezing.

WET is certainly an issue tho, my pomegranate has already seriously objected to the water, fortunately the bed I have in mind is between my patio and a fence so I think plastic sheeting should do the job, I'll just plant the passionflowers (since it sounds like 2 is the way to go) near the pomegranate witch I need to tent anyway

It's those few weeks of near freezing temps with moist soil that might cause the roots to rot. I'd ammend the soil to make sure it's very well draining. Not sure that I'd use plastic to cover the plant. That will cause even more moisture problems. Burlap works well as does landscape fabric or even a good mulching might be enough. Good luck.