With GlamourII I've lately been putting down about 12ml of 1:1 solution per square foot, spread over three thin coats of about 4ml each. 6ml of that total amount is concentrate. Have been experimenting with this for several months. That amount seems enough to provide very robust protection from typical abrasion swipes, while still maintaining good clarity.
That's for glossy canvas. You may need about half that again for matte.
Less than that will leave the canvas texture peaks vulnerable. That's with a good HVLP gun and carefully measured 4" swatches, done to the beat of a metronome, weighing of the gun after each coat. If you're just sort of spraying randomly, you'll need more. And it takes at least twice that amount to do a good job with a roller.
An important caution with Timeless is that it tends to create bubbles with anything except very thin coats. GlamourII does not have that issue and in every way is an easier to use product.
I agree with Dan that a safe number for estimates is about 1 oz per square foot. Remember that for best results you need to put down a certain amount of solution off to the sides of the image, which adds up to a significant percentage of the total when you are doing small prints.
Bottom line is that the water based coating is one of the smaller costs involved in making a canvas print, if you consider materials costs only. But those solvent spray cans can add up fast, especially if you consider the cost of institutional care for solvent induced brain damage later on in life. Have a nice day.