I am not Canadian, and never been denied entry to the US, but I am from a country that requires visas to enter the US (and just about everywhere else on earth outside of the Caribbean

) but I have successfully applied for two different types of US visas. So my advice would be, since your husband has that "black mark" on his book, so to speak, have him act like he's from a non-visa-exempt country and be prepared to show all his ties to Canada:
- job letter saying how much time off he has
- proof of ownership of major assets (car, home)
- proof of sufficient funds to cover expenses for the time you will be in the US
etc, etc. You get the idea. Chances are, he may not be asked to show them, but you don't want to be unprepared if he is. Good luck, and congrats on the family addition!