The wash in type is typically for breathable type fabrics like gor-tex or equal. Spray ons work well too. probably better for heavier fabrics like sail covers etc.
Personally, I would try to web browse sunbrella's sight and see if they recommend a particular product, if any at all. or tents, I have found the spray on silicone based products work best, or coats that are not breathable style fabrics. or my carhart work coat and vest.
I gave up on scotch guard yrs even a decade or two ago. never found it to work waterproofing wise, but did keep stains off! That is my experienc with it.
She drives me boat,
I drives me dinghy!