Eligibility under review means that the first agent who reviewed your case initially has written somewhere in your file "Review Required" on one or more elements of your application. It could be a tiny insignificant thing, just like it can be a major point.
For example, in some applications, agent wouldn't be able to verify duties, and will therefore leave it to a senior agent to make a decision. It could also be tiny thing, for example if the currency in the Proof of Funds documents is unknown to them (Not available in Bank of Canada exchange rates database).
It doesn't at all mean your application will be rejected. You just need to wait for your notes to see what it's about.