H1B Validity

[br8bak]

Currently i am working in a IT services company and on H1B. My I140 is approved in EB2 category and I have completed 6 years of H1B and right now I am in my first 3 years extension window  after first 6 years. I got my Canada PR recently and in order to maintain the status I want to move there for next 4-5 years at least. My employer won't send me so I have to go on my own resigning the job. Now if I plan to come back after my current petition  get expired (which is 2019 Mar) is that Cap Exempt. What are the options that time to get a new extension on that expired petition from a different employer. Will I be able to port my current priority date for my current I140.