FWIW, here's my reaction to these printing materials. (I print and sell only black and white, but I think that is only a minor distinction here.) The bottom line is that I will not be using metallic paper or canvas again.
First, as to metallic paper, I really like the look of it. However, I found that a protective spray destroys the look that I like. I sell prints that are not glazed. This requires a good acrylic coating. So, I was simply not able to sell, or comfortable with selling, totally un-protected prints. For one's own use, this issue would not be a major concern. Just reprint the piece if it gets damaged.
I once did an entire show of "carbon on canvas." (I use high content carbon pigment inks for my B&W prints.) One problem I had was that I mounted the canvas on foam-core instead of stretching it. I did this for several reasons, one being that the inkjet coating seems to be prone to cracking with canvas wraps. However, probably because of the lower ability of canvas (or the high knobs of such) to adhere well to the backing material, I had much more of an issue with bubbles showing up in the finished product.
From an aesthetic point of view, it occurred to me that trying to make my photos look more like a painting was rather incongruous. While I'm in a gallery dominated by painters, I certainly do not need to apologize for my paper medium.
I also am having a negative reaction to canvas wraps, in general, because now Costco is selling too many of them. Canvas wraps are starting to scream "Costco!" Not the image I want for my work.
I also take pride in being able to capture and display fine detail. The texture of the canvas tended to interfere or compete with this fine photo detail. Now this can be an advantage on a very large print that is beyond the image's resolution capabilities, but I found it a negative.
On the plus side, while most canvas products have a mediocre dmax, I found that some are very competitive with paper.
Overall, my mantra remains that (parroting Clinton's "It's the economy, stupid"), "It's the image, ..." that counts. i find buyers incredibly un-interested in the materials and technical issues we photographers/printers obsess over.
Paul
www.PaulRoark.com