Assert what the editor is working on, as its top bar names it: a page by its title ("Home"), or a template ("Utility page - Full content template").
Examples
Then the Canvas editor should be editing "Utility page - Full content template"
And the Canvas editor should be editing "Home"
Then the Canvas editor should not be editing "Home"
And the Canvas editor should be editing "Landing"
Then the Canvas editor should not be editing "Untitled page"
Pattern
Then(/^the Canvas editor should( not)* be editing "([^"]*)"$/, …)
Part of @webship-js/drupal-cms-steps (github.com/webship/drupal-cms-steps), a step pack for Webship-js 2.0.x.