Hi,
Psoriasis is a long-lasting auto-immune disease which worsens in cold climate/changes in the season. Also, there's no known cure for it.... only treatments to lessen the symptoms. I doubt you will get a TRV. You can certainly try though.
Do check if you are medically inadmissible or not.
You must prove that you have the finances to cover the entire cost of your treatment + airfare + any other expenses incurred during your treatment without resorting to Canada's health and social services. Also, your medical condition must not be a danger to public health.
You must include evidence of the course of treatment suggested by the Canadian physician
Cheers