You don't buy a camera, you buy a system
In principle, you could adapt the EF lenses to the Sony camera, but in practice, you can't, because autofocus will be less than ideal with adapted lenses. The only cameras that can use adapted EF lenses and have as good as native autofocus are Canon RF cameras. If shooting wildlife, autofocus performance is the most important characteristic of a lens along with sharpness.
Decide what you want to shoot, and look at what kinds of lenses are available for those systems and what they cost. For example, I have found the Canon 400L/5.6 lens ideal for bird photography when used with a crop sensor camera.
You won't be shooting landscapes and milky way with the same lens so that's at least two lenses you need right there. Perhaps even three, as a fast wide prime for milky way shots might not be ideal for general purpose use.
If you only have kit glass for one system already, don't use that as a criterion; kit glass is cheap.
Next, after selecting the lenses, select camera body / bodies with good enough performance
For example, for shooting quickly moving wildlife, the Sony A7II only has 5fps burst rate and the T7i has slightly better at 6fps. Neither is the best possible available for those systems, but could do in a pinch.
If shooting wildlife with the Canon system, I think 90D is about optimal nowadays. For Sony, I have no experience with those bodies but would pick something better than the A7II limited to only 5fps.
You might need two cameras
When shooting very small wildlife such as birds, you probably want to have either (1) a camera body with huge burst rate and huge megapixel count (extremely expensive), or (2) a crop sensor camera with good pixel density. The latter is cheaper. In fact, it might be cheaper to purchase a general purpose + astrophotography camera and a wildlife camera than a camera optimized for both at the same time.
My current setup is EOS RP (full frame) + EOS 90D (crop) but I don't claim this setup is ideal for everyone. For example, if shooting indoor sports, neither camera is ideal. If shooting indoor sports, the full frame camera should have a better fps burst rate. But I don't shoot indoor sports.