Given we have no definitive idea of your budget, we may offer solutions you cannot afford, so a $value would be very helpful for a body and optics.
The first thing to consider is the body platform (Full Frame or Crop sensor) you will work with as that has a profound impact on the optics you will be using. Full-frame give benefits in terms of dynamic range and noise tolerance, and are better for wide angle work; while crop-sensor bodies are cheaper, are disadvantaged at the wide end, but get a 'magnification boost' at the telephoto end. They are less tolerant of noise and may have lower dynamic range. For wildlife, one might well consider that the R7 is the way to go, but...
IMHO, at every level, any of the R6 FF camera series is better than the R7. There has been a lot of debate out there about the performance of the R7 autofocus, and especially eye tracking, with third party lenses, specifically the Sigma 150-600 Contemporary. There have been claims of pulsing, and Sigma put out a short video claiming their lenses work seamlessly with the R bodies. However, they were using the FF R6 and not the R7.
I personally had no issue using the Sigma 150-600c and 60-600s units, but I was using FF sensor cameras and that is, I believe, significant. The pulsing issue is addressed in a video by bird photographer Duade Paton. Now, while I am not always enamored with his methodology and analysis, the critical thing is the response he received from Canon, which to me is definitive. See: CANON RESPOND, THEIR ADMISSION SURPRISED ME! (youtube.com)
I deliberately chose to go to the FF R5 and R6 bodies rather than the R7 for the following reasons:
While the R7 claims to have a high shutter rate of 30 FPS in full electronic mode, this demands a high performance in terms of image recording, throughput and storage. Any flaw in the data bus will cause a bottleneck and negatively impact performance. I believe that in the R7 this is because, to me, the data bus is seriously unbalanced.
What I mean by that is that the shutter can go at 30 FPS in full electronic mode, but because the sensor is not BSI/Stacked, it's ability to process the recording of the image introduces significant rolling shutter effect, where a bird's wings in flight will look curved rather than natural because as the sensor scans down to record, the speed is not sufficient to compensate for the movement of the wings' displacement. This is also seen when tracking birds in flight, where trees, poles and buildings will look tilted or round objects will look elliptical. Now, this is obviously not an issue if the birds are relatively static, but then one would ask why it is necessary to shoot at 30fps for a bird that's not moving.
The second implication of this is that the buffer is insufficient in capacity and speed for the readout. This means that at 30 FPS, in RAW (which you should shoot in), the buffer will fill up in about 1.2 seconds, and then you can't take any photos until it clears. This is also due, in part, to the relatively slow cards - I would have preferred to see at least one CF-Express card to allow for the fast recording speed.
PIXEL DENSITY: The 32MP sensor of the R7's APS-C sensor has a pixel density equivalent to about 82MP on a FF sensor, something no sensor maker has attempted. As such, it starts to exhibit noise from about 3200 ISO, becoming noticeable at about 6400. Furthermore, given that the R7 has a degraded version of the tracking system designed for the R3, which has a FF 23MP BSI/Stacked sensor, I am dubious that because the sensor is so critical in the focusing and tracking processes, the autofocus is challenged and that may be a part of the reason that several people have had issues with focusing and tracking.
I will say that the system is much more sophisticated than those of DSLRs and thus requires more study to configure and use. To be fair, I think that quite a bit of the negative feedback is from those who have not set up their systems to make the best of the technology for their specific needs. There is a video from Jan Wegener: Canon R7 | The SETTINGS You NEED To KNOW | Fix Most AF troubles! (youtube.com)
The R7 is not weather sealed like the 7D series DSLR bodies, nor does it have a native battery grip - something that I really prefer with long telephotos, for the extra energy capacity, but more for the balance and the duplicate controls for shooting in portrait mode when using big leavy lenses. Again, those are my preferences and may not be relevant for you.
These were MY reasons for not going for the R7, much as I was looking forward to the release of the new body.
On the other hand I have shot extensively with the R5, and R6 series of camera using a wide variety of lenses - predominantly telephoto (I am a wildlife photographer), but also mid and super wide zooms. These bodies are a step up, being prosumer designs, which is your aspiration as I see it. The autofocus is excellent in all versions, they have great weather sealing, solid build and brilliant sensors.
What size sensor is a function of what you will produce as your output medium - for social media, digital display and small to moderate prints the 20 to 24MP sensors are absolutely fine. For extremely large, detailed prints (for for Fine Art) or significant cropping the 45MP R5 sensor is better.
As far a optics go...
If you are inclined to go full-frame, then much depends on your budget. For a lower investment, you could consider an all-in-one unit, the absolutely excellent RF 24-240 IS USM lens. It's Canon's only ultra zoom lens for almost 20 years and it's brilliant. See Search - Canon Community for a list of images from this site.
Alternatively, for long work sticking with Canon, you could go for the RF 100-400 at the cheaper end, but if you took the RF24-240, you could augment that with the equally excellent RF 200-800 IS USM. A brilliant lens for the price. That will give you an unbroken focal range of 24-800mm in two lenses. If you want to go very wide, then the RF 14-35L f/4 lens is an excellent unit.
If you choose a different route, then consider the Sigma 60-600s lens. This is an EF mount, so you need an adapter but it has a massive focal range and works really well with the FF R-series bodies. Samples at Search - Canon Community
cheers, TREVOR
The mark of good photographer is not what they hold in their hand, it's what they hold in their head;
"All the variety, all the charm, all the beauty of life is made up of light and shadow", Leo Tolstoy;
"Skill in photography is acquired by practice and not by purchase" Percy W. Harris
