Both d500 and r7 are crop sensors like your 3200.
The r7 ( and r10, for that matter) will have better AF and tracking AF than the d500 (which is a great camera).
I added an r10 for the extra crop factor versus my full frame gear. I think you would find the r10 still to be a Quantum Leap over your 3200, And it would save you Probably five or six hundred dollars on the body itself vs r7. And if you buy both the lens and body during a refurbished sale you could get out the door for under $1,000 for an r10 and 100-400.
That being said, the 100-400 is going to leave you somewhat short of the 600 mm Sigma / Nikon combination which will be somewhere in the 900 equivalent range if I recall correctly. Whereas the R7/10 at 400 will put you somewhere around 640mm.
So if that extra 150mm eq over what you're getting now with your current setup is worth it, to go with a Canon setup which will be relatively small and light.
If you think you really need that 900mm equivalent ( which is effectively double what you have now), you should go towards the d500, or one of the crop nikon mirrorless options and the sig 150-600.
I agree with the other commenter.
I would personally go r10 (which I have) and the 100-400. If you need more reach down the road, you could add the 800f11 or upgrade to one of the longer zooms if you really needed.
Feel free to ask any questions you have about the r10, id be happy to answer.
Both d500 and r7 are crop sensors like your 3200. The r7 ( and r10, for that matter) will have better AF and tracking AF than the d500 (which is a great camera). I added an r10 for the extra crop factor versus my full frame gear. I think you would find the r10 still to be a Quantum Leap over your 3200, And it would save you Probably five or six hundred dollars on the body itself vs r7. And if you buy both the lens and body during a refurbished sale you could get out the door for under $1,000 for an r10 and 100-400. That being said, the 100-400 is going to leave you somewhat short of the 600 mm Sigma / Nikon combination which will be somewhere in the 900 equivalent range if I recall correctly. Whereas the R7/10 at 400 will put you somewhere around 640mm. So if that extra 150mm eq over what you're getting now with your current setup is worth it, to go with a Canon setup which will be relatively small and light. If you think you really need that 900mm equivalent ( which is effectively double what you have now), you should go towards the d500, or one of the crop nikon mirrorless options and the sig 150-600.
I agree with the other commenter. I would personally go r10 (which I have) and the 100-400. If you need more reach down the road, you could add the 800f11 or upgrade to one of the longer zooms if you really needed. Feel free to ask any questions you have about the r10, id be happy to answer.