Canopy incorporates a backport of Python 3's venv, and is not compatible with virtualenv.
Among the many differences between them are that virtualenv uses "activate_this", whereas venv uses "activate".
Starting with Canopy 1.1, you can use Canopy's Command Line Interface (CLI) to create new virtual environments as either siblings or children of your Canopy User Python environment. More information in this section of the Canopy User's Guide.
We welcome feedback on this current implementation of virtual environments in Canopy, either by email to firstname.lastname@example.org or via the Suggestions / Feedback link in the Canopy help menu (which automatically includes your system and configuration details).