I think departing no later than September 1 from Vancouver keeps you in the good weather window going down the coast.
I have heard about not going south of San Diego before Christmas to avoid the storm season.
Check out 48 North monthly published in Seattle with a column by Dianna Jessie.
Also look at the book Comfortable Cruising by Liza Copeland which is the same trip from Vancouver to Mexico and further.
Coming back in March April is against the wind and current so it is called the Baja Bash. Some people truck their boats north and some leave their boats in Mexico and a few avoid the bash altogether by going to Hawaii on the return trip. Just be out of Mexico by June because of the Hurricane season which runs from June to November.
I wish I could do that trip in the next two years, but it looks like I will still be working and being envious