Some people have luck printing a name from their computer and painting it on the canvas, but too often that results in an effect like a stamped canvas. After all the money and time you invest in a canvas, the only way to have the lettering turn out right is hard work, but worth it.
First decide how large you want the lettering to be. I find it helpful to cut out a blank piece of paper the approximate size I need and placing it where the lettering will be. Next, find an alphabet that matches the design of the canvas. I have a library of cross stitch alphabets (even one in German and one in French) and I flip through looking for the right fit. Look for a compatible design and one that either fits perfectly or can easily be sized up or down.
Now you graph the letters onto graph paper. (I like 13 x 13 graphs, but that means more math when you are painting on 18.). Cut the letters out and place them on another piece of graph paper to adjust the spacing between letters. It’s very seldom that you will use the same spacing between letters. Tape the letters in place to hold them steady
When you are happy with the look and size of the lettering, mark the vertical center of the design area with a straight pin in the canvas. Find the center of the graphed lettering and decide where the bottom of the lettering will be. Starting from the center and the bottom line, count until you reach the first intersection to be painted. Everything else will play off of that start as you paint each intersection in the lettering. Have a small paintbrush and acrylic paint that matches your canvas handy in case you make a mistake and need to “erase” it.
I use a textile marker or acrylic paint for my lettering. (NEVER EVER USE PENCIL OR PEN OR A SHARPIE!) I like to use gray because you can stitch over it with almost any color. It’s a good idea to paint the lettering before you start stitching. You can leave the color choice for thread until you have stitched enough of the canvas to have an idea of what will work. Or if all this sounds like too much math, your favorite needlepoint store can paint lettering for you, even matching previously stitched stockings.