I know this guy from Canada who is here on a temporary work visa. He has offered me money to marry him so that he can stay here permanently. He also wanted a divorce after two years. I know this is wrong and of course I didn't accept it but he also ask another person and she might do it. What should I do?

You can report him to the USCIS or ICE.

You should report it.. there is obviously a reson he wants to get immigration benefits, for all you know he could be a terrorist, you wouldn't wan tto be responsible for that and it is wrong to evade immigration to obscure an immigration benefit, and to use our citizens for that purpose.