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Botanical watercolors are traditionally painted on a smooth ("hot-press") white, cotton-rag watercolor paper.
I've been playing with the various fineartamerica print options, and the one that comes closest to the original feel of the painting is the Somerset Velvet option. My backup choice would be archival matte paper. Both of these will show the detail and the color of the original painting -- the Somerset Velvet has a slightly richer feel to it.
I expected to like the Watercolor paper option, but didn't -- it has too much texture and seems to "fight" with the paintings.
I wouldn't choose either of the canvas choices for the same reason.
The Photo Rag paper may also work well -- I haven't tried it yet. I'd be interested in hearing anyone's experience who has.
So, bottom line: my print recommendations are (1) Somerset Velvet, or (2) Archival matte.
But, of course, you can choose anything you think you'd like!