Peel in the late spring, early summer. If you peel when the sap runs, it is very easy to peel very quickly. Poplar logs are beautiful and great to build with.
You can peel them with a wooden "spud", an axe, a shovel or a draw knife. I prefer the draw knife for tough late fall or early spring peeling, and almost anything for summer.
They will check. If you cut is say June, and peel right away when cut, and let set for about one month while doing all the cutting, skidding and fitting, then they will be OK to build with. There will be not be too much shrinkage, and you should make allowance for one inch, just in case.
From another post of mine,
... then put moss between and ***** with 1/3 each of, sawdust, lime, and flour, mixed with water. The mixture turns out to be just about like cement, only a little flexible, so it does not crack too much. It will last over 30 years that I know about, if you make your eaves big enough to keep the water more or less off - most of the time. ...
Me Mixing Chinking In a Wheel Barrow
This stuff works great, you can leave it unprotected, or varnish it, like we do inside (or outside), I guess you could paint it. You smooth it out with a tough-rubber clove, and kind of work the water to the surface like you do with cement/concrete. You push it in and it stays real strong.
Here is what it looks like installed,
Poplar Walls, T&G 1x6 Pine Ceiling, and Rough 2x8 Pine floor, Pellet Stove, one of Nancy's Braided Rugs.
Chinking Varnished At Logs Below Window. You can see one of the checks, on the lower log, that I filled with chinking (it shows up as a white line - at an angle). The windows had an allowance for two inches of settling above them, and no (zero) settling occurred.
These are Poplar logs (12 to 22 inch-diameter).