Heya,
So ultrawide and 'all around' will basically not be on the same lens, unless by all around, you mean wide angle as the longest in the range. The 17-40 is a good example since you already have it and you know what it's like to go from 17mm on full frame to 40mm full frame. To do that on your APS-C's, you'd need a 11-24. The closest to that is basically the 10-22 which is an excellent crop ultrawide and walk around. The 10-18 is the other option, but is shorter, and comes with IS. Personally I'd want the 10-22, the extra range to me is worth it.
There is the EF-M 11-22 IS STM too ($400 new, you can get it cheaper used/bay) for the EOS-M series if you want a dedicated ultrawide and walk around.
I used to use a 650D + 10-22 as a common walk around, or just my EOS-M + 22 STM (just that lens, no zooms). I found the size difference between the 650D + 10-22 (it's not a small lens) and my 5D + 17-40 to not big significant enough of a difference to matter, so I sold my 10-22 and just use my 5D + 17-40 if I want that field of view setup. The 5D is bigger than the 650D of course, but, not enough to matter honestly. If I truly need a small setup to walk around with, I just use my EOS-M + 22. Powerful and small and I can happily shoot all day with the 22mm (35mm field of view full frame equivalent, a staple to me, wide enough to do it all, but not so wide that everything is dwarfed). These days, I leave all my wide stuff for full frame. My APS-C's are all hugging long telephotos mostly. Full frame just has more options for wide and ultrawide, especially in the fixed focal length categories.
I just let a friend of mine take my 650D + 18-55 STM to Japan for a 5 week vacation, will be interesting to see what he thinks, if it was wide enough, long enough, etc. It's small enough to look "consumer" while walking around. Light enough to not feel like a brick.
One thing that kind of is a bummer is constantly having to have two sets of lenses for the two systems. Wanting ultrawide & walk around on your APS-C's, while already having that on your full frame (17-40). In your situation, why do you feel the need to use the 70D + an ultrawide/walk around, versus your 5D + 17-40 or 24-105?
I generally just use the EOS-M + 22 when I want something compact. I don't have a 11-24 because the space-saving goes away when you put anything other than the pancake on the M series. So for me, M series is pancake-only. The moment I want a longer or wider lens, I just use a different camera.
That said, I'm starting to wonder, do you feel the need to use APS-C/FF for travel & walk around? Why not consider an actual compact camera? Like a G16?
Very best,