Crohn's is a recognized disability in Canada. But just like the US, some people have more difficulty getting disability. I think what throws people off are the questions on the forms that ask what your abilities are. The best way to deal with these questions is to think of what can you commit to doing on a regular daily basis.
Like how much weight can you lift? Think of the amount you can lift no matter how bad you feel. That's what you can commit to.
Another way to think is being at a job interview and flaring with CD. If you told the interviewer that you had crohn's disease and it was flaring presently, do you think they will hire you? Not a chance. They know your health will affect your performance, attitude, etc. It's just the way it is with a serious chronic illness.
When answering questions on forms, don't sugar coat or be wishy washy. If some days/hours are better than others, you must go by the bad days/hours because they are the ones that will intefere with your job and daily living.