How to give photos a canvas finish
Please post a picture showing the type of "finish" you are after.
If you mean giving the texture of a canvas, it's /filter/texture/texturizer, with the canvas option.
Here is something for you with visual process of doing it - http://bit.ly/MQeITF
You can also add a canvas texture image on top of your original. Then use the layers pallet to change the blend mode from normal to multiply.