WOW! I love the idea of the linear actuators! If you are planning on only using two, you will have to perfectly balance the weight of the canopy on the actuators, or you will likely end up bumping into it and toppeling the entire thing over. If the rear sides of your tank are up against a wall, or not too visible, you may be able to put two actuators on each side. I would mount the base of the actuator to the stand, and then mount the moving end to the canopy. You could put two up close towards the front edges and then two towards the back corner. You may need to add some bracing from the base of the stand to the top of the stand, but this would take the stress off of the glass of the tank and re-apply it down to the stand.
I really like the idea that you have, and if you can pull it off, you better log your success with lots of photos! Good luck!