You can paint with watercolors on canvas, it works very well for wet in wet techniques for example. The challenge with painting with watercolors on canvas is that it is difficult to layer watercolors as the previous layers will lift too easily, the advantage is that you can carve lights by lifting up colors.
Here is how to paint with watercolors on canvas and add zentangles.
Start with a rough outline of your drawing with pencil on canvas
A good way to start is to paint a light wash on the canvas, here I mixed a light lime green.
As your wash is still wet, you can sprinkle some alcohol to add textures
As this background would lift very easily, you can fix it by painting plain acrylic medium on top. It will move a bit the paint but once dry will be permanent.
You can then paint another layer on top, here I am painting the foliage letting the colors mix wet into wet.
I also am painting the trunks wet in wet
You can then start zentangling on top of your painting. Here, I did choose designs that had a signification related to trees.
At this point in the painting, it is a good idea to stop for a while and assess the results. For example here I find the trees color to be too pink and blue, so I am adding a wash of green so the color scheme works better for me.
I did add zentangle tothe lower part of the painting with foliage related designs