I built a boat dock in the TN river a couple of months ago and now
I'm ready to prep it and stain it. What products would you recommend
for this process?

First off you would need to clean and brighten then wood. For ease of application we suggest the Hose-Connect Cleaner and Brightener(not the stripper). You need to prep with these cleaners to achieve maximum results with your stain.
Injectable Wood Deck Care Cleaners

All of the stains that we sell are high end without one product that is substantially better then the others. If you are concerned with oil getting into the river then I would suggest the Defy Stains:
Defy Stains

If that is not a concern to you then I would suggest any of the stains on this list. I may be able to narrow it down for you more if you have concerns with color, mold, penetration, etc.
Deck Stains and Sealers

You may want to look at the CretoWood as a pre treatment to your stain. This is a one time application that prevents internal rot and decay:
CretoWood Permanent Wood Sealer