In my experience, a wood like poplar doesn't make for durable wear surfaces. A flexible, but tough finish would be best. Spar varnish is made to move with the wood, but it scratches rather easily. Epoxy finishes move enough, allow quick buildup for toughness, and scratch less. The last time I used epoxy finish, I used the system 3 epoxy finish. I think they changed the name, but it is available from Lee Valley.
It is a somewhat expensive answer, any other ideas?
I'm sure others will add their experience but I'll share another resource. Their is a great site dedicated to finishing at www.homesteadfinishing.com visit the general finishing forum and do a search on poplar and you will find a ton of advice from toning down the green to various types of finishes. Good luck with your project.