I am a pernament resident of the USA, my Green Card has expired but I have a letter of extension for one year. My aunt died in Canada , can I visit using the extention letter?

Yes you can

Yes you can. You must apply online for an eTA if you are traveling by air (I put the expiration date adding the 18 months the extension letter says). Print the approval they send to my email . And when the travel agent ask for your "visa" present the eTA email.

Hello there I'm lebanese and have a permanent residence with valid lebanese passort can visit my son in Toronto also do I need another documents.

yes you can with your extention letter and a passport.