If by "soffit vent channels" you mean the styrofoam trays you fit between the rafters before covering with fiberglass insulation, vapour barrier and drywall, then...

Consider installing extruded polystyrene insulation instead. Not only does using polystyrene foam insulation eliminate the need for those styrofoam trays, but it gives you much better R value. Fiberglass will typically be R=3.5 per inch, whereas extruded polystyrene will be R=5 per inch of thickness as a stabilized R value. So, if you have 3 1/2 inch rafters, and you devote 1 inch to ventilation under the roof sheathing, then 2 1/2 inches of extruded polystyrene is going to give you R=12.5 versus R=8.75 for fiberglass. That's a 42 percent increase in insulation.

If you opt for a 1/2 inch air gap under the roof sheathing, the difference in R value is even greater; R15 versus R10.5.

But, be aware that in order to add ventilation to your roof, you will need to cut through the shingles at the ridge of the roof to install a ridge vent. If you don't have a ridge vent now, it'd be best to save this work until you need to replace the shingles on your roof, and add a ridge vent and ventilation at the same time.

Answer this question, tho: On the coldest F***ing day of the winter, if you go into your attic, do you see any frost or condensation forming on the underside of the roof sheathing. If the answer is no, then you really don't need to add ventilation to your roof. You've got as much attic ventilation as you need to prevent damage and adding more isn't going to do any good.

Contrary to popular belief, attic ventilation is used to prevent condensation occuring in the attic in winter. While attic ventilation can also cool the attic in the summer, a super hot attic in summer won't do any harm to your house, whereas condensation forming in your attic in the winter can cause serious and extensive damage to a house. So, regardless of what you may have been told, the reason for attic and roof ventilation is to prevent condensation forming on the roof sheathing in winter, not to cool the attic in summer.