I'm going to quote part of what Jeremy Pierce recently said about the fate of the Canaanites:
I don't see holes in the patience theodicy merely because some are given more chance than others. First, it may well be that God has knowledge of what these embryos would do if given a life, and it's less severe for them to die this way or would lead to a worse fate (in terms of being evil people) if they lived. I wouldn't assume such a thing, but I also wouldn't rule it out. More helpfully, perhaps, I'd say that we need to be aware of the various possibilities for what happens to those whose lives are cut short (even aside from the embryo situation). Many Christians think they have an afterlife befitting never having had moral capabilities. So I wouldn't assume that the patience theodicy needs to consider God as being less patient with them than with Hitler.
Then there's the insistence that most Christians would have that it's only in the afterlife that the scales really get evened out anyway. Also, if everyone deserves judgment, and no one deserves patience, then it may be unfair in some strict sense to give some people more time and more chances, but it's not as if those who deserve worse than they get can complain. According to the judgment theodicy (which was the one I thought most powerful, not the patience theodicy), most people suffer less than they deserve. That's why I think it's a more powerful theodicy, not because of anything to do with God's patience or the relative distribution of the effects of God's patience. There are a host of questions that need answering before you can make the judgment that there are holes in this theodicy, and it depends very much on the particulars of the version of it that's being made, something I've been pretty silent on at this point, since I want to claim that a wide variety of views could try to make use of a punishment theodicy.
The arbitrariness charge also assumes that we know more of what's going on than we possibly could. God could have reasons related to what will occur in the afterlife, secret facts about this life that no one or almost no one alive today knows, truths about what individual people would do if they had been presented with certain counterfactual situations, and maybe even intrinsic goods that we don't have much understanding of at our level of development. God might intend certain results and thus allow benefits to someone who doesn't deserve it for reasons entirely apart from whether the person deserves it. I wouldn't expect us to see the difference as to whether this is arbitrary or calculated, but a theodicy isn't supposed to be an attempt to show what actual reasons God has, just what reasons a divine being might have in order to show that the problem of evil doesn't disprove (or make unlikely) God's existence. If there are possible explanations, then it doesn't. If there are likely enough explanations given God's existence, then it doesn't make God's existence unlikely. If what we were going for is an actual explanation, this wouldn't come close. But that's not how the problem of evil's dialectic goes.