What under-eaves vents can I use to maximize attic airflow and minimize insect infiltration?
I live a couple of hours south of you.  I installed a heat activated powered vent in the roof.
Our house was miserable in the summer at night.  You could feel the heat radiate from the ceiling.
After adding the powered vent that turned on @100 deg F the house was comfortable in the evening.
They have solar powered vents now , so power would not need to be run.
The powered vent was much cheaper than adding the vents at the soffits, and being close to the ridge it removed the hottest air.