Technologically if you can map every connection you can upload the mind.
The trick is every connection is more than just every neuron. Not only is it possible we can do it for simple brains, the only limitation for humans is how difficult the mapping is and the fact it is 100% destructive, so you get one try. Mapping a fruit fly took years and hundres of people and AI. So if you want to get around it in story just use the risk to the brain angle. The gamble is still too high to risk destroying a brain mapping it if it could be lost through a single error.
the other issue is if you could map the brain without destroying it, it starts diverging from the original brain in the first few minutes as you learn new things and thuse the pattern changes. so you can use it to predict a person that well, and it gets worse and worse as time oes on. If your goal is upload a person to say provide an alternative to a dying body then the only real arguments are politcal or ethical not technological, you could do it. The connectomes we have of fly brains appear to perfectly predict behavior so there is no reaon to beleive it would not do the same in humans.
The firing sequence basically resets when you sleep so you the sequence is not really important if your trying to recreate "you". You just loose everything they learned since the scan, but it makes prediction less and less possible.
Now as Nosajimiki pointed out you also need a receptor map, neurotransmitter and hormone receptors, but that is doable too. We have already started doing it. its up to you what the limits of your technology is.