We have 3 nice heads of red cabbage to pick soon. We are most likely going to can it all as sweet and sour cabbage but before we do that I was wondering if there are other ways to preserve it using the canning method.
We most commonly braise it under some confit duck legs. That recipe is altogether more complicated than the method we use (usually just a bunch of herbs, an onion or two and some red wine, not red wine vinegar) but I'd start with theirs and simplify.
Like a lot of fresh veg, it can be frozen if you blanch it first. Essentially cut it up, boil a portion for 90 seconds, cool it rapidly, dry it and then seal each portion in a vac-pack bag before freezing it. This is great if you have unlimited freezer space... And you really like cabbage.
If you're desperate to can something —per the question tags— I'd either confit some duck thighs in duck fat in some cans (what the French do, seriously though you need to try duck and cabbage together), or do some pickled cabbage. It needs quite a sweet pickle and it's not as nice as pickled beetroot (that'll probably attract a downvote) but it's still a worthy sandwich stuffer.
If you get really bored of pickled cabbage, you could throw the rest of the allotment in, and make a piccalilli. Great way to hide some cauliflower and it keeps forever.