Yes, OneDrive is secure. To learn more about how OneDrive safeguards your data in the cloud, please read this article from Microsoft.
You do not need to use a VPN to access your files on OneDrive. You can use the Microsoft web interface to securely access your OneDrive files from anywhere in the world.
The simplest option for accessing your work files from home is to upload them to OneDrive. OneDrive is available to all staff, students and faculty at the University of Toronto, and you can access it through the Office 365 web interface.
To learn how to upload your computer files to OneDrive before you work from home, access OneDrive training through the University’s SuccessFactors website.