Was landing with the canopy open common back in the day? I know it probably was during WWII, but during the transition to the jet era...?
Yes.
IIRC, in the late 60s within the Training Command, while the 2-seat TAF9J usually (but not always) landed with the canopy closed, the single-seat AF9J usually landed with it open.
However, while instructors were allowed (mandated?) to land with the single-seat AF9 canopy open, SNAs were not at my time, for some unknown reason.
Also the ejection seat was far from "zero/zero" and in the 2-seat trainer model, the seats went through the canopy upon ejection. Don't remember about the single seat.