It's a good question of course and narrowing it down can be helpful in certain regards though I was never so concerned to go that far because the differences in varieties are not as important as the quality of individual stems so its important to go through and pick out the ones you want personally before its milled. For example the Alba version is normally good for nothing but were you to find a stem that by chance had grown good and straight and not to fast, (fat chance), with a good trunk, that wood will be a bit harder than black poplar even. For the rest, Canadian, Black, Italian... the considerations are all similar in its use. Where I come from the Cottonwood, a kind of poplar, is native and in the town and properly trimmed will grow straight and tall but in the natural habitat, out there in the desert growing next to a seasonally running water, it will branch out near the ground and so produce only reaction wood. If you've got space for storage, or can make it, this is a handy wood to have around for many uses and I will always try to have it milled up given the chance because the last poplar I got had been cut short for firewood and like Richard writes it's not the best wood for burning.