I am assuming that you are the Canvas Admin.
You can use the Redirect LTI to add global menu items that point to external web sites, so if those items are web-based or n a web-server, this is relatively very easy to do. We use this to add links to our Library resources, for example. You can even specify that the links populate at the course-menu level.
Learn more at Redirect Tool
That site discusses using the Redirect Tool at the course level, but it works exactly the same at the account level.
I hope this is helpful,