You can cancel the smash attack and the cannon shot with a roll in order to gain momentum. And you can keep momentum by bunnyhopping. (Hopping as soon as you hit the ground.) If you don't jump as soon as possible, you'll lose almost all your speed.

The timing for rolling out of smash is very quick, whilst out of a cannon shot you have to wait for (Or just before) the cannon shot.

I'm also bad at explaining.