Dena,
Just to complicate your choice for Sunday, I really enjoyed the "Faaroa River and Island Exploration". We went on this excursion mainly for the stop at Marae Taputapuatea, but ended up enjoying all aspects of it ---the motorized outrigger canoe ride on the Faaroa River and the 4x4 jeep ride to the interior of the island. The guides were very interesting. But, there's no snorkeling, which I know you said you were wanting to do a lot.
I agree with those who enjoy the Bora Bora motu. In many ways, I enjoyed it more than Mahana --- better beach, not as crowded, better swimming, spectacular view. Key is to have the blow-up rafts as there are no chairs. There is a nice coral formation for snorkeling. Your plan for the Bora Bora Off Road Adventure in the morning on Wednesday is good, rather than in the afternoon. It won't be as hot. Then you can enjoy the motu again in the afternoon.
Also, we really enjoyed the Trails of the Ancients Trek with archaeologist Mark Eddowes on Moorea. It includes a stop at the Belvedere lookout which, if it's not foggy, is a great view of the sacred mountain Rotui and the two bays. The "trek" is a walk through the jungle to various ancient sites (although some have not been excavated). Stay close to Mark as to not miss any of his narration. The walk is through some rough terrain and quite fast-paced! It was very interesting if you want to learn some of the history/culture/and traditions of the islands. But, again, no snorkeling.
The decisions about what to do are tough to make. But, whatever you end up doing, I think you'll have a wonderful time.