Dear Alberto,
Applicants who have a condition that might reasonably be expected to cause excessive demand on health or social services in Canada will likely be refused a permanent resident visa.
Diabetes Type 2 is not in and of itself a reason to refuse an applicant if the condition is under control.
If an immigration officer decided to refuse your application on medical grounds, you would still have the right to contest the decision and submit a second medical opinion from a doctor of your choice (naturally one qualified to speak to the questions in dispute).
This response is for information purposes only.
Jukbo