I don't think you'll be discriminated against. Much of medicine is easy to practice from a wheelchair. Surgical fields would be difficult to break into, but not impossible.
I've met a number of med students/residents with spinal cord injuries (PM&R is a common field for them to gravitate to). We interviewed maybe 3 or 4 for an SCI fellowship, including one who required a full-time assistant because she had a complete/near complete tetraplegic SCI.
I don't know how many of them had their injury prior to medical school vs during med school or residency. So that could play a role.
If your disability is a big part of why you're choosing medicine, then I'd recommend writing about it. If it's actually not a big factor in why you chose medicine, it's certainly ok to leave it out--you do not have to disclose your disability in your personal statement. There are other areas in the secondary applications where you could likely bring it up as well, but it's also not required.
If there is a question on the application asking "do you have a disabling condition that impairs your ability to practice medicine" then you could write it there, though many would argue you'll be able to practice medicine just fine and wouldn't need to. In your case your disability is something people will be able to easily notice because of the wheelchair (unlike with severe depression, other severe mental health issues, chronic pain, chronic fatigue, etc.), so I would argue it's best to err on the conservative side and answer something to the extent of "I have a T12 incomplete spinal cord injury and because of this I rely on a manual wheelchair for mobility."