I think that the 7D2 would be the best upgrade. They can be found for very reasonable prices and the camera has a number of significant upgrades over the 7D, starting with a significantly improved AF (65 all cross-type AF points compared to 19), 10fps, much better high-ISO performance, and faster processing, among others. It's really an impressive camera, even in these days of mirrorless bodies. I use mine alongside my R6 and have no intention of getting rid of it anytime soon. If you were to invest in a mirrorless body you can still use your lenses with an EF-RF adapter, which works extremely well. There is no degredation of performance at all, and many people feel like their older EF lenses actually perform better on mirrorless bodies with the adapter. I use all three lens types on my R6, EF, EF-S, and RF, and the older lenses perform beautifully! No need to rush into mirrorless though. While I am smitten by my R6, I still love my 7D2 and would feel perfectly fine using it as my primary camera if I had to. It's a lot of camera packed in a professionally rugged body (Canon considers it their pro crop sensor body) and to get the most out of it you'll have to be willing to spend time learning all of the settings and ways to fine-tune and customize it to your liking. It's a great camera straight out of the box, but it's a phenomenal tool that you can grow into for quite some time when you learn all of its capabilities! Hope this helps a little.
Andy