"Can" Vents Acceptable on Low-Pitched Roof?

Hi, I'm who posted here yesterday asking about metal roofs. The price in our area is significantly higher than for shingled, but the homeowner has all the problems associated with "walk-up" hip vented roofs: improper ventilation, resulting in mold.
Contractor #1 low-balled the others but will not take off the unvented soffits, even though he claims he's going to replace ALL the plywood decking. When I asked how this would be possible without removing the gutters/soffits, he said he "thought" our gutter system was suspended from the fascia... His not knowing whether or not this is the case, in addition to his real nervousness when I asked the question, makes me skeptical of using him.
HOWEVER, he says can vents will solve the problem without the need for new vented soffits.
Contractor #2, big-cheese roofing contractor who talked us into 9 feet of ice shield as opposed to 6, tells us how good his "system" is, tells me he's too "old" to go up into the walk-up attic (early 40's), then offers a 95K bid for basically a tear-off and new soffit/gutters. NO DECKING INCLUDED WHATSOEVER.
In his opinion, can vents will insure destruction of new roof because of flashing issues as well as the fact that can vents aren't part of his unique "system."
I've had at least seven roofing "contractors" through the property. Price is an issue but not the most important, which was why I asked about metal roofs yesterday on another thread. What I need to know, because a choice will have to be made between *one* of these charmers (I suppose) is: ARE CAN VENTS ("POP-UPS") STILL ACCEPTABLE ON MODERN ROOFS? WILL A LOW PITCH (70'S RANCH HOME) ON THE HIP ROOF INSURE PROBLEMS WITH CANS NEXT WINTER?
We live in the Poconos in Pennsylvania, at an elevation with--pardon the language--bad-ass winters.
Thank you.
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It appears each contractor is "designing" his own system. I suggest you look at two web sites and set your own standards. NRCA (National Roofing Contractors Association) has lots of construction info. Building Science Corporation has researched climate specific systems information.
How does the first contractor know he has to take off all the roof sheathing? Have you been in the attic to check for leaks and deterioration that would suggest that is needed? IMHO, a low sloped roof in the Poconos needs ice & water shield. If the under roof area is to be vented, it is my belief that soffit vents with ridge vent is the way to go.
TB
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