Canvas, even the smoothest weave, will have a 'tooth' that will hold your paint. But, I've found a few small tricks have helps me when I need a smooth canvas (and don't want to use a board).
-Clean your canvas before you stretch. A finer weave, higher quality canvas won't need this.
-Apply gesso with your hands instead of a brush. Once you've stretched the canvas over your frame, massage the gesso into the canvas until you have a nice, even layer. Sometimes using a brush can leave streaks that will turn hard and leave rough textures.
-After your layer of gesso had tried thorough (wait a good couple of days), take a very very fine grit sand paper and giving the surfaces a very light once over. This will rid you of bits of gesso that may have clumped and of any bits of canvas that you may have missed when cleaning. Be careful! If you sand too hard or too much, you will reveal the canvas and have to re-gesso.
But, if you want smoother than this, you'll need to go to a prepared, hard surface.