I recently completed a project (a bed frame with rolling storage drawers to go underneath) where I bought a mixture of true poplar and tulip wood (which is marketed as "poplar" even though it is a completely different species). They came from a local lumber yard. They are considered more or less interchangeable from a commercial standpoint. They do generally have a substantially different appearance, but that doesn't matter because probably both mostly get used in painted projects or for internal parts that don't show. I had never worked with either species before.
If "poplar" has green, gray, purple coloration and a distinct grain pattern, it's probably actually tulip heartwood. I understand that tulip sapwood is a lot lighter and better resembles true poplar, but I don't think I got any of that. Long story short, I liked working with the tulip better than the poplar. The tulip was noticeably harder and denser. It planed more consistently. Mine had a lot of green in it (which would reportedly turn brown over time if exposed to UV light) and had a pronounced grain pattern that grew on me (the boards I worked with were all flatsawn, so they had cathedral grain). I might consider using tulip in a ukulele build, but I'm not sure poplar would be my first choice for that. One the other hand, it appears to be a perfectly fine wood for a bunch of purposes, including the ones you described.