Hi, and welcome to the forum.

Direct from the horse's , um, mouth

>> These Canadian citizens traveling to the U.S. require non-immigrant visas:
* treaty traders (E)
* fiancé/es (K-1)
o and the children of the foreign citizen fiancé(e) (K-2)
* a U.S. citizen's foreign citizen spouse traveling to reside in the U.S. while awaiting final completion of the process of immigration (K-3)
o and the children of a foreign citizen spouse (K-4) <<

Though that's for Canadians looking to reside in the US after marriage to an American. If you're splitting your time between the countries, you may be able to sort things out after the wedding. (Or just stay in Canada until the US paperwork is sorted out.)

Best thing to do would be to contact the US Consulate in Ottawa directly. Here's their website : AMCITS • Consular Services at the U.S. Mission in Canada - they list a phone number you can call (though, as they say, have your credit card ready - it's billed by the minute).

You may also want to contact the Canadian Consulate in DC to find out if your intended needs any particular paperwork to travel back and forth with you.

Congratulation, by the way.
Cheers,
Bev