From what I read you are going to buy a camera + lens. And these brands are good and popular too. Also a good lens+ a reasonable good camera is better than a good camera + cheaper lens. So recommend don't buy the cheaper kit lens.
And back to you questions, because you are looking for the DSLR type camera, it looks like you’re interested in photography as a serious hobby. Keep in mind, if you buy the mirrorless camera, Sony a6300, you should know you can't use the regular SLR lens on the mirrorless camera except with the adapter, like you had the canon SLR lens, you can buy the EF-EOS M, I used canon camera so that I follow its news. I am not sure other two have the same type adapter or not.
For the lens, you should ask yourself what is your primary use for? landscape? ( for most of us )? wildlife photography? portrait photography? etc. And if you want to know then google each categories for what lens recommendations. Keep in mind, you should always buy the best one you can afford. Also try to find the review on the lens you are interested in. Like
Other side notes: you will need a tripods ( good for anything, buy a good one too, means it can support the weigh for your camera+ lens), an extra camera battery, shutter release cable, or the camera bag too, filters: recommend GND and circular polarizer only. If you want to take sunrise/sunset, or moon rise/set photo, you have to use the apps for your phone to find the good spot. Or web site for PC, this site is easy to use ( IMO) https/www.suncalc.org
Here I added the linker for three cameras side by side comparison. https/www.dpreview.com/products/compare/side-by-side?products=canon_eos800d&products=nikon_d3400&products=sony_a6300