From the 1994 edition of the A-6E Intruder NATOPS, canopy airspeed limits were:
Opened 250 KIAS
Opening 200 KIAS
Closing 150 KIAS
Of course, if you had the canopy open, better safe the seats since the canopy frame would be right over your head.
BTW, had the canopy pop open an inch or so or...