Most inkjet canvas is a poly/cotton blend.
I use both Matte and glossy canvas, Lyve and Crystalline both by Breathing color.
I prefer glossy canvas, just like the look for my work.
For matte canvas, I always coat with Timeless, also by Breathing color. With Crystalline/glossy I will coat depending on where the print will be located. All aqueous based printers, HP, Epson, or Canon, the ink on the canvas can be lifted if you get any water an or moisture on the face of the print. Coating the front of the print gives you an added amount of protection. For hospitals, or other office buildings, I always coat a glossy canvas as you never know how the print will be handled and if it will exposed to the public constantly, (hallways) or rarely, (conference rooms).
You will find that there is no right answer to these questions, it's a matter of personal preference.
I have had EXCELLENT support from the guys at Breathing Color over the years and they make great canvas. They also have their own mill. Epson, and Canon do not make their paper or canvas products, it's all jobbed out to 3rd party mills. Some feel this is not important, I have decided it's very important.
Paul