Gina, I am not adding anything to Peg's comment. I am making some technical obsevations.
This is a quote from Ralph Mayer's book,
The Artists' Handbook of Materials and Techniques:
"Size is considered an absolute necessity; oil paint should never come in direct contact with the the fiber or the canvas will "rot", that is, eventually become weak, brittle and crumbly."
Ralph Mayer's book is a well respected text among serious artists who are conscientious craftstmen.
If you want a canvas tonality, thinly glaze with Galkyd or Liquin, in your color choice. Let it dry, and you have a warm color surface that can be sucessfully overpainted.
I would also check the aformentioned text on the problems of applying canvas to a panel.
Sincerely,