Since you said your trip & hunt takes place in September. Any bear taken is going to have a far amount of additional summers fat to get thru. I wouldn't use a HP but the heaviest jacketed SP available like Hornady's 265 gr Interlock SP should be sufficient for the purpose. Powder that's a matter of what's available these days. Although Win 296 & Hodgdon's H-110 are the same. But, H-110 is indeed coated with graphite and requires a LP Mag primer to fire it up. I personally would use Win 296 as its powder is much easier to ignite and it isn't coated with graphite. Win 296 normally requires just a Standard LP primer for its ignition.
Which ever way you decide to go in regards to powder is fine. Keep in mind Black bear especially large ones are indeed tough animals to kill. This type of hunt is all about first shot placement. Raised in Northern MN where Black boars sometimes get to be well over 400. I do have some experience with Black bear. Good luck and enjoy your bear hunt Sir.
"Do not follow where the path leads, rather go where there is no path and leave a trail for others to follow."