Well assuming you are an Australian passport holder you are visa exempt to return to Canada but to fly into the US you will need to apply for an ESTA at the official US government site. If entering the US via a land border then you fill in an i94 at the border.
For your return to Canada just make sure as well as your passport you have your permit to hand to show CBSA if asked given as a temp resident you still need to be cleared to enter the country each time so the work permit shows you have a valid reason to enter.
No idea about Cuba although thought read somewhere they issue visas on arrival but you will need Google that yourself.
