Established businesses and/or indirect competitors will most probably not bother getting into a partnership with you, at least until you start having some traction and results. Many startups have the ambition that they will build great partnerships starting from day one and they often get dissapointed. No one is going to do the sales for you. You will have to prove your value first and then ask for permission for partnerships.

Having said that, should you have the luxury of getting a big partner on your side from the beginning and they are really committed in helping you, you have to estimate the ROI of their support to you. But that's a different discussion..