If possible join a club and find some decent material. Don't know what you have there but maybe a club can arrange some digs for suitable material. I imagine it's cold up there but one thing that comes to mind is Amur maple which makes a good bonsai. Maybe it can be found in a local nursery but certainly on-line. or find other cold hardy species.
It is difficult and time consuming enough to develop a deciduous bonsai from raw material from a suitable species much less a large leaved coarse tree with long internodes.
I imagine this post will draw fire but I do not expect to see a good bonsai from these species or some of the others that have been posted lately. You don't see the experienced members on this forum touting these odd-ball species.
I don't care if you are 19 years old, spend your time with decent material. Time is shorter than you think.
I'm 22 and have plenty of very high quality material.
My poplar are more so of experiments, which I've proved quite a few people wrong on quite a few things about them.
For instance, they have big leaves and long internodes, I've changed that quite drastically in only one year.
I've actually had my teacher who was a student of Ben Oki tell me a year ago that they are worthless and no good for bonsai. Last week she saw mine and literally was mad at herself for giving up! She said "good job Aaron, you proved us wrong!"
To here that from a women with 50 years of experience, tells me something.
One question, have you ever tried a poplar and ACTUALLY gave it a chance? Probably not, just like many others.
I'd love to post a pic of my tree but it's been growing out for a few weeks to gain energy for winter. I'll pot an update on my thread of the tree though.
I'll continue to use this "trash tree" as many call it, and I'll continue to enjoy it!
Happy bonsai
Aaron