with leaf scars=:
narrow raised;  terminal buds=hairy;  buds have hairy inner-scale between 2 outer-scales or
crescent-shaped, with 3 bundle scars, centered above is side bud scale :

Leaf scars=crescent-shaped, with 3 bundle scars, centered above is side bud scale

terminal buds >25 mm (>1 in), fragrant, lots of resin, twigs=red-brown
balsam poplar Populus balsamifera or
balm of Gilead Populus × jackii

terminal buds about 12 mm (½ in), egg-shaped;  twigs=gray-to-brown
swamp cottonwood Populus heterophylla
terminal buds about 12 mm (½ in), ∨ ∧ tapers at both ends;  twigs=yellow-to-yellow-brown
eastern cottonwood Populus deltoides