I have been using Ampersand Claybord Art Canvases for my watercolor cityscapes. I've come to prefer this surface over heavy watercolor paper, although I still use Arches paper if I want to paint a more traditional watercolor.
The Claybord surface behaves much differently than watercolor paper, but I enjoy the characteristic effects that can be achieved. Also, the color can be completely lifted off and the surface can be lightly sanded in order to banish any areas of discontent. You can also really mess up your work if you unintentionally drag a wet sleeve or swipe a watery brush across your completed work ( I have done this and it is horrifying, so be careful with slinging water around your work area.)
After a painting is completed, I use Kamar Varnish made by Krylon to seal and protect the painting. This also adds a bit of shine to the painting and enhances the brilliance of the watercolor.
The downside is that the panels only come in standard sizes. Luckily, though, the manufacturer makes panels with square dimensions, which I like to use for my "Where Squares."
There is also an option to use flat or raised panels. The raised panels are great if you don't want to add a frame. When I frame the flat panels, I "stack" them on layers of mat board instead of putting them behind a mat opening. This is very doable because of the solid surface with nice clean edges.
I have added a series of photos showing the painting progression and final results of my Old Courthouse painting that I completed recently. This is a 16x16 watercolor on a flat panel framed to a size of 22 x 22 inches.