It's my feeling/experience that various Poplar trees yield equally medicinal buds to use for medicine. I've used quaking aspen, bigtooth poplar, eastern cottonwood, black poplar, and have used the oil of the balsam poplar which is delectable.
If you're out gathering and you find a couple different looking species, there should be enough dried leaves around it to give you an ID. The buds are also telling, of you have a good tree book.
I'm fairly confident that most other types of Poplars around the US would give good sticky buds, it just takes a good day spent wandering in the woods, somewhere near water.
The Eastern Cottonwood (Populus deltoides) is distinct - it is often extremely tall, towering over riverbanks and putting out early swollen buds that you can see from a further distance than other trees' buds. The bark is, to me, like a ribbed sweater.
The wood is weak, and tends to litter many twigs and branches on windy days or from a heavy snow.
In the summer, they release clouds of "cotton" into the air, creating a magical summer "snow".
The quaking aspen (Populus tremuloides) is a smaller tree, usually growing in groves with male and female trees close by one another. The early buds that open from the once sticky bug-like capsules, are soft fuzzy buds, like pussy willows. They are all under the umbrella of the willow family. Quaking aspens also have a lovely white "bloom" on their trunk, which is the sloughing of the bark cells, and it is rich in lactobacilli. Bark expert Michael Wojtech told me that you can make a sourdough starter from it!