Got a work offer but asked for my first visa digits

This sounds like a scam to me. The first 6 digits of a Visa card number identify the issuing bank, who they can now call, and armed with the other identifying information you have given them, can try to social engineer into transferring money out of your accounts.

You should look in a reputable Canadian phone directory for the main office number for the company you think you're talking to, and call them to see if the person you've been emailing there actually exists, works there, and has the authority to offer you a job. I also think you'll find that immigrating to Canada is a lot more involved and drawn out (some people wait years) than the process you're describing.

Its a scam: https://arstechnica.com/information-technology/2016/12/thieves-can-guess-your-secret-visa-card-details-in-just-seconds/

The numbers can also be inferred by combining your first six digits—which are based on the card brand, issuing bank, and card type—with a verification formula known as the Luhn Algorithm.