Yes, you can—but only after you’ve added VoiceThread to one of your Canvas courses. You have to take this first step in order to have your VoiceThread account created under Miami’s license.
Afterwards, you can go to voicethread.com/login and sign in with your MiamiOH.edu credentials. Just be sure to select Sign In With Email on VoiceThread’s log in page; the Find My Institution option will just direct you to Canvas.