Until I read, you are looking for a location outside of USA, I was going to suggest start in the Florida Keys. Doing a part of the Adventure Cycling Southern Tier ride wold work.

I would do some research at crazyguyonabike. You will likely find information about location options and maybe some help for the tour in general.

My wife and i have been touring consistently for over 25 years. I think you are making a great choice for traveling together.