I've used both Canon and Sony cameras over the years. I started with Canon, used Sony for a while, and am back with a Canon EOS R5. The Sony cameras are very nice, produce phenomenal image quality, but the mirrorless camera bodies of the A7 series are just too small for me to hold well. They may be a perfect fit for smaller hands, but the larger DSLR-style body of Canon's mirrorless R5 is pretty much perfection for my size of hands (not huge, but not small).
Sony's Exmor sensors deliver exceptional image quality. The latest line of Canon sensors is getting closer. The R5 sensor is generally of the same class as the Exmor sensors, although I think the edge still goes to Sony in the end. By image quality, I am referring to resolution, sharpness, dynamic range and color quality. I find that dynamic range can be quite important with pen photography, as highlights are often very bright (even when spread out) while the darkest shadows can be very dark (especially if you are using darker backdrops for your photos.)
I've been with Canon since about 2008, and even when I was using Sony cameras, I largely stuck with Canon glass. Their lenses are second to none, produce exceptional quality and sharpness across the field. They are built like tanks, easy to use, and last for a lifetime. This is, IMO, the biggest reason to buy into any particular system. Sony is growing their collection of lenses, but IMO they just aren't in the same class as Canon. Nikon has some excellent lenses as well, but again, Canon just has the better quality and a broader range of lens types, including a variety of specialty lenses like the MP-E 65mm macro lens, which is useful for close up photography of small things (i.e. bands, finials of pens), or their range of tilt/shift lenses, etc.
I fall in the middle when it comes to DSLR vs. Mirrorless. I have used and owned both. I currently use and own both, although I do use the EOS R5 the most. Ironically, the EOS R5 is the most DSLR-like of the mirrorless cameras I have used, and I LOVE it. I was a DIE HARD fan of a proper optical viewfinder for a long time, but the most recent Sony A7 series and EOS R5 camera EVFs have changed my opinion. They are wonderful, being able to see your exposure real time with your eye to the viewfinder is awesome, and all the extra heads up display stuff is great. The EVFs are such high resolution these days, you can't see the pixels anymore (one of my biggest complaints of the past), and the color depth and dynamic range are just about as good as an optical viewfinder now (I think the R5 EVF is better...just love it).
I think it is hard to go wrong with either a Sony A7 camera (i.e. the A7 or A7r are the best options imo, the A7s tends to have huge pixels which reduces resolution, although they are great if you need to photograph in much lower light), or a Canon EOS R5 (and maybe the R6). I think the prior generation of Canon DSLRs are great as well. The 6D and 5D series are great. The 7D line, never quite had the image quality, always seemed to be rather noisy, and did not have good dynamic range. I've owned a couple of 5D series DSLRs, and I have liked them all.
Oh, I will say this... I think all the cameras I list above are FULL FRAME cameras. This means their sensors are 36x24mm in size, so twice as large as your average "Rebel" type camera, and even larger than some other popular cameras. This larger fame makes it a lot easier to get closer to your subjects and get the most detail and dynamic range. You should be able to find a Canon 6D series full frame DSLR or a Sony A7 series mirrorless used for a pretty good price these days, and IMO having the larger sensor is worth it.
