Well, there's the historical answer that the objective military situation at Chancellorsville was pretty horrid for the Confederates, something well described by Edward Porter Alexander in his memoirs.
But game-wise, there's probably some detail of what you're trying to do/how you're going about it that would be helpful in giving advice: i.e. what difficulty, are you trying to win on Day 1, or going through the historical progression and executing the flanking attack/dawn follow-up? What is your Corps composition like, how much has the union been able to progress beyond the minimum army size in the campaign so far, etc?
My experience is that winning on day 1, once you know how it flows, is much less taxing, but if you don't know that's what you're planning to do right off the bat it's not particularly easy - both because you're attempting to hold an objective in the middle of the open with all of the Union reinforcements spawned basically on top of you, and because you need to secure the farm until the end of the ~1-hour 'contested' period, so if you lose control of the farm for 1 minute after the mission timer is over, that puts you instantly into the next day, which thus doubly sucks because of the extra attrition taken trying to hold the farm in the first place.
Regardless of which phase, I've found that the Union position is best approached from Hazel Grove, as you can flank the one fortified building within the wheatfields from that direction and that avoids the fences and woods everywhere else. That does require staying out in the relatively open ground, though, so I usually accompany that with a nearly exclusive focus on counter-battery fire from my own artillery from the get-go - Usually of the 48 brigades available, I'm bringing at least a dozen batteries of 10-pounder parrots along with 5 or 6 other artillery batteries and 2 or 3 sniper detachments with TS Whitworths which can sometimes knock out a battery or two but are mostly for spotting duty.