Happy to hear that you are moving forward to give your bag a chance at an upgrade in leather
Like others have mentioned, if you can, maybe visit a different boutique, even one inside another department store (like Neiman Marcus or Bloomingdale's), or go the mailing-it-in route. I would still try to get the leather replaced via LV first before taking it to another company or getting the bag altered into those boho style bags.
As for the canvas, looking for something that has little creasing and isn't super faded is good. I have definitely used leather conditioner to wipe down my canvas (Apple brand) and it did not dry it out at all. Even just a gentle baby wipe I think helps to reduce dullness.
I hope you get results with LV and I can't wait to see the finished product!