Extension tubes have no optics. Just get a set that have electrical connections. No reason to spend the dollars on the Canon version.
AFAIK, Canon has not released a set of extensions tubes for the RF mount. If they have, B&H only has third party tubes, which just might be okay...and then again they might not.
Both are capable of producing excellent macro shots (if you define "macro" as no more than 0.5X magnification). Your expected use(s) should probably determine which one to pick. Both have comparable IS and both are exceptionally sharp.
I own the RF 85 f/2 and it's becoming one of my favorite lenses. like all longer lenses, it has less perspective distortion than a wide(r) angle lens because of the "flattening effect" of the greater working distance. The focal plane is, of course thinner at any given aperture, but for most macro shots these days focus stacking is used instead of small apertures, so that can actually be an advantage for the sharpest images.
The longer working distance also makes subject lighting much easier in most situations. I also own an EF 35mm f/2 macro which I've used on both EOS R and EOS R5 with adapter. For my applications, which are typically 3-dimensional objects like jewlery, insects and flowers, I use the 85 f/2 90% of the time. The available working distance makes it much easier to light subjects and the RF 85 f/2 is also a superb portrait lens. The 85 mm's IS on a R5 is amazing and hand held shots at 1/5 sec with a still subject are usually sharp. Alternately, the 35 is also useful as a nice landscape lens.
Since both are great at other uses beyond shooting macros, I'd suggest that you consider your other possible applications in your decision process.
"But I'm debating between the canon 85 and 35. Your thoughts?"
Neither lens is a true macro but either one beats extension tubes, IMHO. Simply because a lens can focus somewhat close to a subject does not make it a macro. A true macro lens is a different lens design.