Since direct SSL certificate pinning for check.torproject.org and torproject.org (curl method) (T80) would have to wait a long time, until Debian stretch, this ticket is for an alternative approach.
Please make sure you've read T80 first.
mitm suggested in the forums to:
Learn from the code for downloading while direct pinning TPO's certificate from launcher.py (see VerifyTorProjectCert).
Seems the most promising method for now.