The crab nebula is magnitude 8.5. That's very dim. To image very dim deep sky objects like the crab nebula, you're going to have to do things a little differently than your current approach.

Rather than a lens, you almost certainly need a small telescope with a much wider objective than a 24mm f/4 lens, which has an entrance pupil of only 6mm in diameter. A small Newtonian reflector typically has a 10cm primary mirror. That's almost 17 times in diameter and 278 times more area to collect 278 times as much light as your 24mm f/4 lens. It will also typically collect that light from a narrower slice of the sky, which is also what you need for tiny targets such as M1, which has an angular size of barely one-tenth degree (6 x 4 arcminutes). Your 24mm lens shows about 60 degrees of sky diagonally, or about 600X the size of M1. So at best, at 24mm you can hope for the crab nebula to cover only about 10 x 8 pixels on your 70D's sensor.

Even then, you're going to need pretty dark skies to pull magnitude 8.5 objects out of the background sky glow. If your sky is dark enough, longer exposures with a tracking mount can capture such dim objects, but getting them onto the screen in Live View in real time is probably a pipe dream.

What you can do is use the brighter objects nearby (like, for instance, Aldebaran) to aim in the vicinity of your target and then take a test shot and examine the results to see if you're aimed where you want. If you're using a tracking mount set up properly, wherever the scope is pointed will be maintained while you're looking at your test image(s).

You can also use the brightest stars in the sky to manually set focus. I will "barrel sight" my lens at the brightest star in the sky and move the focus ring from past infinity back until the star is visible and as sharp as I can get it. Even with the brightest stars, if they are out of focus by very much the light from them will be spread so thin that you won't see anything at all. I'll then use 5X magnification to refine focus in very small adjustments. I'll then use a slightly dimmer star at 10X to get the focus as sharp as I can.