My husband was denied access to the US 2 years ago over a conviction 30+ years ago for pot possession.. just wondering about getting a US waiver and how to go about it as I understand it is a complicated process.

Yes even though the pot conviction is over 30 years old and it was just a joint, the Americans can still deny you entry to the US.  Since you have already been denied entry to the US then you will need a US Entry Waiver or I-194 to return to the US.  A US Waiver is only good for five years and then you will have to renew it.  The US Waiver application is complicated and expensive but it is very possible to obtain.  Speak to a counselor at Pardons Canada at 1877-929-6011 x1