A good properly exposed and printed B&W will look good on both, but sometimes the subject matter, will uh,matter. A foggy morning landscape would look good on canvas, where as a stark shrape image of a building might look better under Arcylic, which can act as almost a lens and adds a 3D effect, on the few images that I've seen so far on/under Acrylics,
I haven't seen the acrylic but the canvas has a texture. Depending on your image the texture may or may not be acceptable. The acrylic has a smooth finish and I would expect it to compliment a photographic image just as glossy photographic paper does.
Right you are! I've seen only 2 large Arcylics and have been impressed with both! I print an awful lot of my stuff on canvas, mostly because of the cost savings and I also use a very smooth canvas, which has almost a "luster" feel and look,