Funny you should ask. I just developed some tendonitis in my wrist and I'm going through a similar situation. I just picked up a wrist splint/brace and after having worn it for a full day now, I can't really foresee being able to wear it while riding. I don't think mine will allow me to ensure a proper grip on the handlebars. I'm afraid that my grip might slip and encourage me to lose control in fast traffic or bad roads. Also, I'm finding that if I inadvertently fight the brace and try to bend my wrist farther then the brace allows, it causes some pain. I can see this situation being exacerbated while biking. For now, I will ride without the brace until I get used to wearing it while performing simple tasks. My doctor didn't specify whether I should wear the brace while cycling so I will wait to see what the physiotherapist says next week. All that to say is I'll ask my physiotherapist if he knows of any braces which may be suitable for sports/cycling. If he has an ideas, I'll let you know.
The splint I'm using now is the MedSpec Wrist Laser Wrist Support.