You can enter US as a touist to file I-485. Then, file I-131 to apply for advance parole (AP) at the same time with I-485 filing. It may take about 5 months or longer to get AP approved in these days due to Covid 19. You cannot leave US before the AP approval.
So, if you cannot wait for AP approval, you had better ask your employer to file I-824 for you to apply for immigrant visa in Canada, not come back to file I-485. Talk to your lawyer for assistance in this case.
