More canoes are destroyed by flying off a car than are wrapped around rocks. (Western Canoe Company factoid)
Best is if you have roof racks.
A: Secure mid point of the canoe to the back of the roof.
B: Secure the stern of the canoe to the rear bumper, preferable as close to the corners as possible.
C: Secure the other end of the canoe to the front bumper.
Don't cheap out. Use nylon rope. It has a bit of stretch to it so that it doesn't go from tight to floppy with the relaxation of 2 mm. 1/4" (6 mm) or 5/16" (7.5mm) is sufficient. It can be twisted or braided. Polyester rope has very little stretch. Sisal and manilla rope change dimensions if they get wet.
These work well too. If you have long lengths of ratchet strap in the wind, they vibrate like crazy. Put about 1 half twist to 1-2 feet to reduce the vibration if you find it annoying. Ratchet strap hooks aren't as flexible for attaching to either the canoe or the car. In some cases you can use a rope loop at one or both ends.
I don't like the camlock straps. I've had those loosen up on me on several occasions. I have more rope than ratchets, so the rest of these instructions deal with rope. Adapt to your situation.
Run a line with several turns around the crossbar, using a knot like a pipe hitch, double catspaw, or prussik. The idea is you don't want the rope to slide on the cross bar. Wrapping the bar with wrinkly duct tape or hockey tape may make this easier.
Repeat on other side. At this point you have two ropes attached to the roof rack crossbar in a way they can't slide.
One rope should be short enough to not reach all the way across the canoe. Put a bowline in the end. Run the other rope through the bowline, pull hard and tie.
Repeat the above steps for the other cross bar.
No roof rack.
You need to keep the gunwales from scratching your roof. Canoe stores sell foam blocks for this. You can also take a pool noodle, cut into 1 foot chunks, slit one side to the hole in the middle, and clip this around the gunwale. I have also used life jackets. PITA.
Open the car doors.
Run a loop of rope through the body of the car and over the roof. Put two loops that are the width of the canoe apart, (A figure 8 knot tied on a bight works well) OR tie a series of knots (figure 8) a few cm apart so that there are knots around the gunwales when you put the canoe on top. Tie this rope loop firmly. (Same technique as above, put a loop in one end, run the other end through, pull and secure.)
Now you have a rope with a high traction surface. Treat the rope like you did the cross bars, and tie to it.
Having knots in the rope on either side of the door opening so that the whole loop cannot shift once the door is closed is a good idea.
Secure to the car's corners. Some cars don't really have a bumper. You may need to go underneath and secure to the frame. If you will be doing this a lot, you may want to add tie down eyes on whatever you do have at the corners.
Do not tighten this yet. Get snug though.
The wind force on the canoe is going to try to push the canoe back. If the bow is in front of the bumper, then, if you tie to the bow, you just pull back more. Canoe slides, and ropes go slack.
Instead use the bow seat as your tie point. Tie to a corner of the car, take a turn around the seat, go over the canoe, take a turn around the seat on the other side, and down to the corner. The idea is that the turns around the seat keep the the rope from sliding forward, and the loop over the bottom of the canoe takes most of the strain off the seat.
If the bumper is unusable, open the hood (bonnet) secure lines to some part of the frame, and run out under the sides. There is going to be strong forces on these lines. Take care that you don't damage your car. The hood is latched only at the centre. You want to run the ropes in a way that doesn't pull up on the corners.
At this point the front ropes are vertical or sloped back toward your windshield. If they are sloping forward, you need to move the whole canoe back on your car.
Tighten the ropes. Roof, bow, stern. If you are using foam blocks or noodles, you want to see them squish. If using a roof rack, pluck the ropes. Play music on them.
Often once you get going, things loosen up. Drive 10 km, and stop and check.
I've had canoes turn on my roof, due to the canoe sliding back, and loosening the front lines. This will put a substantial sideways force on the car. If it happens rapidly, you may have an interesting time. The smaller your car, the stronger the effect.
I had a canoe try to escape when the front line broke (sharp frame)
Stop and check at 10 km, 30 km, and every time you stop for to 'rest' and buy petrol.
In passing, I'm impressed with a 4 day workshop that can produce a 22 kg 17 foot canoe. This sounds fragile. That's a light canoe even made from modern composites. Run these directions past your instructor. He may have additional comments.