I would suggest you contact the American Consulate in Canada and discuss this with them. You would most likely need to ask the consulate general for permission to let your husband immigrate.

You can apply for a visa, sponsor him as his wife, a legal US Citizen. When approved, they'll call him to come and pick up his papers at his local embassy, and he'll be able to enter the country legally.

You need to apply for it. Two ways to do it: If you and your husband live in Canada you need to go to a Us Consulate and put in papers for an I-130 petition (cost around $400) you need to be in line an hour before the consulate opens and wait your turn in line to put in the paper for the application, within 2-3 weeks they will send you a packet in the mail giving you either an approval or declinal of the petition. Once approve you have more papers to fill out and return them to the Montreal Embassey, then you will get another packet of papers, in these you will have to fill out an affidavit of supprt (meaning you have to be able to prove you can supposrt your husband 125% above the poverty line for the state you live in) he has to do a medical exam (mainly they want to make sure you do not have any STDs, or major medical issues) then you have to fly to Montreal to sit in an office and wait for an interview to recieve a visa allowing him to live in the US, this is the green card, every 5 years he will have to re new the green card until he takes an exam and pledges oath to the us and becomes a citizen, this usually takes anywhere between 6months to 18 months to do from start to finish.