Generally, if you have a medical condition that will require treatment, you will not be allowed to immigrate in to Canada. Period. Canada does not want additional burdens on it's health care system.
If you were already in Canada, while seeing a doctor is free (more or less), drugs are not, so, you would have had to pay for HIV meds. This depends on the province one is in though, as each has it's own system. In some places there are fees, but, not in others.