I speak from personal experience here...I spent almost two years in a wheelchair, and still have to use it occaisionally. I am a former police officer, who was injured in the line of duty, and as a result, am now retired.
First, as Mr. Pincus mentioned, the weight of the pistol will be born by the chair. Concealment will likewise be handled for the most part by the chair as well. This makes carrying a full-sized fighting handgun possible, practical, and to me....preferable.
Typically, I carry a GLock 19 or a Glock 30 in an IWB crossdraw holster with spare magazines in a similar crossdraw magazine pouch to the left of the gun, while in my chair. It is easily, and rapidly accessible AND comfortable. It conceals well for a couple of reasons. First of which is when you are in a wheelchair....you are invisible. Face it...people give us a quick glance, then look away as if we weren't there. "CUN CARRIER or ARMED CITIZEN" is the last thing MOST people will think of as they try not to see us. While in a wheelchair, cover garments are even more effective, as the clothing tends to bunch up, or fold differently. This is an advantage to us. Third, while in the chair, NO ONE notices a jacket over your lap, or any other such "handicap" aid that we may be using.
I use the same methodology while using my powered mobility scooter. The scooter seat has no arms, and my usual holster placement on my right hip isn't as discreet as it would be if I were walking, so I go back to IWB crossdraw.
As for choice of weapon...I carry a Glock because in my personal experience, they have been 100% reliable. I have literally hundreds of thousands of rounds down range from my various Glock models and have never had a gun-related malfunction. I can't even say that about my Wilson Combat 1911, or my Sig P220. The ballistic payload, 16 rounds in a Glock 19, or 11 rounds in a Glock 30, make it a weapon I can engage a target with, and not have to further manipulate the weapon as often were I to carry a revolver. This is just my personal choice. No one who is good with a wheelgun is ever undergunned, unless he is facing someone who is good with a rifle!
I don't know the extent of your physical limitations, but I have full use of my upper body and all my upper body strength.
I practice weekly on my home range, and I practice from standing, and from sitting. I practice strong, and weak hand, and on multiple targets. Handicapped doesn't mean VICTIM.
Best of luck, I mean that.