Can I paint with watercolors on canvas?

Absolutely! But first you will need to prep the canvas with a watercolor ground. Lots of videos about the product and how to do this. It can be very pretty!

Hi Bonnie. There is a special canvas for painting with water colors.

I did this with acrylic paints by mixing the acrylic paint with a medium that was something like modge podge and it gave the perfect transparency to the background texture I put down and only tinted the canvas so that it wasn't so stark white. Check with a hobby store for what is that works with the acrylic paints. It has been too many years since I painted to remember what it was, but it turned out just like you want to do to your painting.

I water down my acrylics (especially if I am adding shadows or highlights) or add a transparency medium.

You can, and you have to do the watercolor first. There is a medium that thins out acrylics, in case you don't like how it turns out. I can't remember what its called, liquitex or something like that. You can also mix in small amounts of water at a time to thin it some so its not so heavy