140 current but not in USA or old job

Hi,
I was on H1B Visa, and my employer applied for my I-140 in 2018. Later I resigned from that job, and joined a different company in Canada. I am now in Canada with that new employer.

Questions:

  1. If in future, if my current employer agrees to relocate me back to USA, and file my I140 again, will they be able to use my old priority date so that I do not need to start from scratch in the waiting line for green card?
  2. What happens if my I-140 becomes current, WHILE I am in Canada? So let’s say that in 2 years, my old I-140 becomes current. Is there still a possibility that I go back to USA from my new company after 4-5 years and try to make use of the old I-140 dates, to apply for i-485?

Once I-140 is approved for more than 180 days, unless USCIS revokes (for reasons like fraud etc), your PD is available to be ported with any other employer sponsoring your GC and filing your PERM & I-140 in future.

I-140 petitions do not expire (unless revoked by USCIS) which means there is no actual time limit governing how long a person could wait to move forward with an I-485 filing.

Your new company will need to restart the GC process (PERM → I-140 → I-1485/AOS) but can port your priority date from old I-140. If your priority date is still current at that point in time, your employer can file I-140 & I-1485 concurrently.