We use Canon at work and I use Sony for my own use (used to use NIkons, and way back in the old days of manual I used Canon). Using Canon at work is mainly a legacy thing, a long while back that’s what was used and since we already had the lenses (which is where the real expense comes in), we were kind of locked into that platform.
DSLRs have a vastly better battery life than mirrorless, so you don’t have to carry as many of them, which is a big bonus if you’re spending a lot of time in the field.
DSLRs tend to be much more bulky than mirrorless, even the lenses. This means more weight, more space used, etc, and this can be a problem when traveling, or doing foot-based fieldwork. Often (not always) DSLR lenses are more expensive too.
In terms of image quality and such, at this point almost every camera on the market can produce images better than anyone other than serious professionals can distinguish between.
The Sony mirrorless cameras are excellent, and Sony in particular has been producing some of the best lenses on the market recently. A big advantage of Sony is their low-light performance and their video, which is good enough that the documentary teams I’ve worked with in the last few years have all used Sony A7s as their primary cameras when filming.
I usually carry 2 cameras, a Sony a7III and the a6500 (I’d get the newer one that uses the larger battery that the a7III uses, but I can’t justify buying a new camera just to have the battery interchangeable between the to cameras). The great thing with this setup is that the lenses are interchangeable and that the a6500 is small enough that if I have a small lens (or even the 50mm macro) on it it’ll fit in a large jacket pocket, or a small waist or shoulder bag.
Generally I have a long lens on the a7III and a macro lens on the a6500.
My suggestion would be that if you plan to be in the field and away from recharging options for more than three days of heavy camera use at a time, the go with the DSLR, otherwise go with the mirrorless.
No matter what you’ll be needing extra batteries. Also get a shoulder sling. They’re much more comfortable for carrying the camera than the neck strap. If you’re on foot and using long lenses, a hip holster is a good idea too. I use one when I’m out walking with my 200-600mm lens and it makes a huge difference in ease of carrying it.
Your lens choices will be a major part, if not the primary part, of what drives your decision. Think about what lenses you need (and want), and what the costs for those are on different platforms. The camera body is almost secondary to the lenses these days, and is a temporary purchase (eventually it’ll be upgraded), but the lenses are more of long-term investment and the money spent on those will vastly outweigh the cost of the camera body.
Also, mirrorless cameras can use (via adapters) lesnes from any DSLR platform, but DSLRs are locked into using only (with a few exceptions) lenses made for that camera type. This has to do with the space between the lens mounting ring and the sensor.
EDIT:
It’s worth mentioning that DSLRs tend to have faster wake-up times than mirrorless. Mirrorless are getting much faster though, so that’s not nearly as big a difference as it used to be.