It is really serious

You will have a interview and you will be asked some questions. CIS people will find out that you having been working in Canada. Do not cheat. US people hate those who cheat. Once they ask you to show the employment letter, they will know and you will be not able to get the green card.

You did not tell them the truth ever you already knew and you had to.

It was not raining when Noah built the Ark. You need to think about it.