I've never found many bones in canned mackerel.
I hate to find bones in fish, and if I do, it transforms my eating experience from joyful to tentative at best. I pick through every flake looking for the offending articles.
I've recently been doing my own mackerel, from fresh and the way I clean and fillet it (thank you YouTube), the chances of any rough bones remaining are much reduced. Once you've done a couple you become much faster at the whole thing, and they only take a few minutes to cook in a pan, on the BBQ/Griddle or a little longer in the oven. Baked in foil with a little salt and chilli on top, with a squeeze of lime juice), they're delicious hot or cold.
Off the BBQ/griddle the skin can be spectacular.