Its totally fine to look for customers on this website. I'm sure many E30 owners here cruise USA classifieds looking for a E30's anyway.
Your car is worth more in Canada than USA IMO. This is because clean rust-free examples of these cars are harder and harder to find up here, and I cant imagine this car fetching $4k in the US.
....Only downside is the cost of getting this car up here and time involved. That might balance out the difference and make it easier for you do sell locally. ~1200 miles is a long trip to pick up a sub-4k E30.