My three-year-old cedar fence looks dry and some of the cross supports have cracked. My main concern is to protect the wood from further damage. Is there a product that would recondition the wood without requiring staining?
If a sealant is the answer, would it need to be stripped if I ever decide to stain and seal it later?
A sealer is not going to keep the wood from cracking like you describe. It sounds like it is fracturing as it dries and was likely not seasoned well when the fence was constructed.
A sealer will arrest the weathering of the cedar and you can stain over it later. However, look for a sealer with that capability in mind if you think you might be doing this soon. Thompson's waterproofing products, for example, have a liquid wax as the basis of their chemistry and you will not be able to stain until it weathers out---usually 8 months to a season.
I would look for sealers with crude oil composition for your sealing application. The good news is they are relatively inexpensive. Those with vegetable oils might be a good second choice but they will have some sheen to them and they could be harder to stain over. Hopefully Sherwin Williams has added them, at least on a special order basis, in their stores too if you don't have an MAB store near you.
If the fence is already weathered and you want to balance out the color, I would consider an oil-based semi-transparent stain that will seal and blend the appearance all at once. I would cringe if you went near Olympic paint (they should have stayed out of the business) but their semi-transparent stains are alright and I have used them for years. MAB, a Sherwin Williams company, offers my fave products.