Hi Melissa
You can take Marine Dr. off of Balboa Island and make a left on Bayside Drive, cross over PCH and ride through Newport Dunes to Back Bay. Once through Back Bay you can take the San Diego Creek Trail up to Irvine. The traffic you would encounter would be on the very first part of the ride and very minimal.
If you want someone to ride with when you're here, give me a shout. Tiffanie and I are just north of Newport Beach, in Huntington Beach!