I don't have specific knowledge but I can offer an educated(?) comment.
Guitar, there seems to be to be a steady flow of rare guitars on eBay so this could in fact be a good place to sell such an item.
Morrisseau, I wouldn't think artwork of this type is that suitable for eBay. For this specific item I would contact Kinsman Robinson Galleries for a comment. My sister is into the Morrisseau stuff, she has three pieces purchased from Kinsman Robinson, from observing it can take a considerable length of time to find the right buyer willing to pay the right price. I've also occasionally looked on eBay for his works but I've only seen a few of his small "low end" pieces offered.
I suspect that the Guitar has a very established "market price" as it is "rare" but not "unique". Art pieces on the other hand fluctuate in value considerably depending on the flavour of the moment. With all the recent exposure this is probably a very good time to move the Morrisseau.
Although the price might be too steep for my sister, if you send me an image I could pass it along for her comments, I think she paid around $15k for the last piece.

"What else could I do? I had no trade so I became a peddler" - Lazarus Greenberg 1915
- answering Trolls is voluntary, my policy is not to participate.

"What else could I do? I had no trade so I became a peddler" - Lazarus Greenberg 1915
- answering Trolls is voluntary, my policy is not to participate.