Does pentoxing (waterproofing) my bamboo sticks posel it to be kosher sechach in any way?
No, waterproofing a bamboo cane will not invalidate it from being kosher for use as sechach, and this can be done lechatchilah.
Only a change in the form of the sechach, so that it is not recognized as something that has grown from the earth, or a change that renders the sechah a utensil (such as etching a hollow into a plank of wood), invalidates the sechach (see Mishnah Berurah 629:12).
Based on this principle, a number of authorities rule that there is no problem in using painted wood for sechah. Although the paint is made of material that is not kosher for sechach, this does not invalidate the wood, because the paint is tafel (secondary) to the wood, and becomes a part of it. See Shut Maharia (5); Shut Ha-Elef Lecha Shlomo (Orach Chaim 364).
Shut Machazeh Avraham (Orach Chaim 134) goes a step further, and explains that even if wood or canes are coated with a material that is not kosher for sechah, such as a metal (gold, for instance, to beautify the sechach), the wood remains kosher for use as sechah. Provided the coating is a thin layer alone, it is considered part of the wood, and does not invalidate the sechach.
Rav Shlomo Zalman Auerbach testified (Minchas Shlomo Vol. 3, no. 151, citing from Rav Charlap) that the wood used for sechah by Maharil Diskin was coated with colored paper as a decoration (see also Shalmei Mo’ed 26).
Based on these sources, there is clearly no problem with using waterproofed canes. The waterproofing does not alter the appearance of the canes in any significant way, and the material used clearly becomes part of the cane, so that there is no question that the waterproofing process does not invalidate the sechach.