Medical Certificate
All pilots flying in controlled airspace must have a category 4 medical certificate (and have passed the HAGAR exam). For those pilots that have no medical conditions, this can be obtained by completing a Category 4 Medical Declaration and sending it to the local Transport Canada office. It may take up to 40 business days to get it back.
If there is a history of cardiac disease, or any other medical reason to doubt fitness for flight, then a civil aviation medical examiner (CAME) needs to make the decision whether one is fit for flight, and sign off on the category 4 medical.
Specific medical requirements for the declaration are here, in the last column.
A fillable category 4 medical declaration can be found here, or as a standard PDF here.
This Medical Declaration does not expire by itself, as long as what is on it is valid.
A list of Civil Aviation Medical Examiners can be found here.
The Canadian Aviation Regulations reference can be found here (CAR 602.29 3 (ii)).