Hi Parent,
I hate giving blanket answers due to all the details involved in everyone's own situation, so I'll give my usual answer, which is maybe. I say that because normally swimming and operating a handcycle wouldn't seem to be affected by having an ostomy. But your specific body type can have an effect on things. Those who have loose or uneven skin where the stoma is placed have sealing issues with their barrier. What I'm trying to say, but don't want to just come right out and say is if you're fat and have loose or flabby skin or skin folds where they place the stoma, you're going to have sealing issues if the seating position of your handcycle makes you sit upright, rather than lying down. Swimming with an ostomy barrier that you're having trouble adhering to your body won't be fun either. I'm not assuming you're overweight or have loose skin on your abdomen, just saying if you do, you're gonna want to talk to an ostomy nurse for his/her opinion as to whether you might have barrier sealing issues with your specific body.
Not related to swimming or cycling, but just dealing with the day-to-day care and feeding of an ostomy... you mention C7. If the mobility and dexterity of your fingers are compromised to the point where you can't manipulate the barrier and bag, you're going to need someone to help you with your barrier and/or bag changes... maybe even emptying your bag. I don't know if that's something you consider a non-starter, a minor inconvenience, or have no issue with.
From a health standpoint, an ostomy can be a great solution for some folks, but physically can be tough to manage. So it depends on what your "bowel issues" specifically are and what the prognosis would be if you got an ostomy. Does it 'cure' the issue or just buy you some time? And on the physical side... is an ostomy something you can handle the care and management of? Sounds like you need to have some serious conversations with your Gastro and Colorectal Surgeon and an ostomy nurse... because while it's easy to say an ostomy is great and won't affect what you want to do... the devil is in the details, as usual. So sorry I don't have a simple answer for you, but neither your condition nor the question are really that simple.
;O)
bob