I would like to fill cracks in my Garage Floor but they
Are about 2-3" wide and about that deep. What Can I
Use to fill and then to seal and paint the garage floor?

Those are some big cracks, is the floor heaving underneath? I would investigate why the floor is cracking before you repair so your not re-repairing it in a few years. For a crack that large you should probably use concrete to fill them. There are a lot of garage floor paints, epoxy paints are best for this.

This is a very bad signal of movement and horrendous settling. The crack will likely continue to grow so you must find out what is wrong before you consider patching anything. If the crack is 3" on the surface and then narrows to almost nothing 3" down that is a sign of the perimeter foundation settling more than the center of the floor.

Call an epoxy floor contractor. I install epoxy floors in Michigan and they are difficult to apply for the average homeowner. The floor should be scarified prior to applying the epoxy. Many companies etch with muriatic acid instead of scarifying or shot blasting, but in a garage (heavy use area) etching is not as effective. The epoxy can be mixed with cabosil (powdered fiberglass) or other high build aggregate which turns it from "paint" to "putty" to fill your cracks. I use Florock by Crawford Labs 100% solids epoxy. It works great and lasts forever if you do it right--or at least 10 years because that's how long I've been doing it. It's kind of expensive (about a $1000 job plus a couple hundred more potentially for the crack repair for a 2.5 car garage--usually about 22x20) until you compare it to the cost of a new floor. The cracks can take a lot of material to fill depending on size. I'd be happy to lay out the entire process if you are interested. Don't use floor paint in the garage!! It will peel up in a couple months or sooner, especially where your tires are. Hot Tire Pickup-- When you drive on the hot asphalt roads and then pull in the garage and plant all that weight in the same spot every day your tires will stick to the paint and pull it up when you back out. 2 coats of 100% solids epoxy (done correctly) is the only thing that works in a garage. Sherwin Williams Armorseal is another brand that is readily available. Make sure you know what you are doing if you are going to try to tackle this yourself. The 100% solids epoxy has about a 40 minute potlife so you have to get it out of the bucket immediately after mixing it. You pour it into a pile on the floor, squeegee it and then roll it with a high quality roller cover with a solvent resistant core.