A friend of mine gave to me an used canvas of some jewelry or perfume advertise. Although I had better wished she introduced me to the model, I thanked her and decided to make a fast wood frame and hang it on the wall. It's a very simple instructable, but anyway it could give you some cue to reuse a nice advertising poster.
You need to take measures of the canvas, and assume a thickness for the wood profiles. If you don't find the right thickness, remember that the more thick is the profile, the shorter its length should be. This is because you have to turn down behind the frame the edges of the canvas.
If you buy the wood frames in a shop with cutting service, you could make the cut the right length, and avoid some work with hacksaw and angular guide.
Then you need a staple gun. Mine is very cheap because I rarely use it, but it's very handy if not essential for some projects.
Put all the four profiles at right position, and check they form a perfect right-angle rectangular. You can glue them together and keep them in position with some paper-tape.
Now fix them shooting one staples on the first side and two staples on the opposite side. In this way you'll be sure that the staples don't interfere one to each other. Then you can remove the tape.
Check the size is right for your canvas. Try to pull the edges to see how much inside the frame they reach, so you could pull them on the right position when you'll begin shooting the staples.
When you know how much pull and where the canvas edge should arrive, you can begin blocking a short side with one staple at time. Finish all first short side then begin with the opposite side. Here you have to pull a lot the canvas, then lock it with your finger and shoot the staple... not on your finger! Complete with this method the second short side.
Before fastening the long sides we have to make a consideration. The long sides are much more flexible, because they are pulled with the same force of the short ones, but they're much longer, and we know that momentum goes with square of length. So we have to reduce their bending length. To do so I've cut three pieces of an used plastic guide for electrical wires. Length of these shafts should be exactly as the inside of the short side of the frame.
Put these three shafts at equal distance inside the frame. You don't need to lock them because when you'll pull the canvas they'll stay firmly in position, and they prevent to bend frame when you pull hard the canvas.
Now complete the fastening of the long sides, with no worry about the flexibility of the frame.
When you've completed all the four side maybe you want to remove the first and the third shaft, and leave only the center one, in my case I've noticed that now they didn't make so much force on the frame, only the center one is now needed.
Your poster is now ready to be hunged up on the wall. I've used double side foam mounting tape, because I think frame is light enough, but maybe you want to add two hooks for two nails.
My living room is reserved for my huge panoramas, so I've banished her in my kitchen ;-)