I've had back and hernia surgery, both related to moving cannons in my younger and more careless days. Now with cheap powerful equipment avialable, no one should suffer those injuries, but they still do.
There are many good ways to move cannons so what's pictured here isn't necessarily the best, but it is one that (at least in the steps shown) puts no dangerous stress on the human body.
The 2-Ton hydraulic shop cranes as shown come from Harbor Freight and are about $180. for a handy type with folding legs, which only takes up a few square feet of floor space when stored.
Some cautions using the shop cranes: Adjust the boom length to more than the load you are lifting (there are 4 positions which wll handle various loads.) Work on level pavement if possible, never work so the crane is inclined to one side or other. If inclined back or forward, use something to brake the wheels or it will roll on you.
Never roll them with load elevated, they tip over easily. The wheels are only put on these things to move the unloaded crane around. Lift the load then back the vehicle up under it, then lower the load. If you absolutely must travel a short distance with load on crane, lower the load so it rests on the two crane legs, or better, on a pallet you put on top of the legs.
Any rigging scheme is OK as long as straps, chains etc are rated to handle more than the load, obviouosly. The rigging using straps which is my personal preference takes shape in a form depending on what length strap(s) you are using. Chains are easier to use but I don't like to mar the paint or the bronze on a cannon. I like to put a strong piece of steel tubing (not much smaller than bore diameter) in the bore so I have a shoulder formed by the muzzle to hold the strap in position.
Once the cannon is inside the van, I secure it from moving forward by connecting the cannon to the trailer hitch using a strap (not shown in photos.) If you don't do something like that, the cannon will come up and visit you in the driver/passenger area the first time you have to apply the brakes firmly.
Other methods work also, ramps and winches or come-alongs, etc., and I've used 'em all. Forklifts are great too but I can't keep one at home. Be safe.