I am not very familiar with Canvas LMS but based on your description it sounds like they restrict JavaScript for security reasons. as you mentioned CSS pseudo-classes and browser events would normally help in this case but it seems those are not possible given the limitations.

One suggestion I can offer is to use the title attribute for the words you want to display the tooltip for. It is a basic solution with limited styling through inline CSS but it does show a tooltip on hover and might still be useful.

Good luck!