I have created a Portfolio Canvas and other users are not able to see it who have the same access that I do and are displaying the same context in the context bar. Are created Canvas' only visible to those who created them?
Unfortunately the Canvas (Labs) functionality doesn't have the ability to share out canvases with others at this time. One workaround I've done for this is use the Business Model Canvas functionality (exists at the Portfolio level). You can mimic the same content boxes as the Portfolio Canvas template and Business Models are accessible by all users. Give it a shot and let me know if you have any questions. Here's a link to the help info on Business Model Canvas: