At present Canada Visitor Visa Holders who are Parents or Dependent Child or Spouse(Husband or Wife) of a Canadian Citizen or Canadian Permanent Resident (PR) can travel to Canada. Other Canada Visitor Visa Holders cannot travel at present. Parents whose son or daughter is on Student Visa or Work permit Visa in Canada, cannot travel unless they have obtained a special clearance from Canada.
Parents and Child having valid Visitor Visa do not need to show any Special Reason. They can travel to meet their Canadian Citizen or PR Son or Daughter for any personal reason or may be just to stay with them for no reason at all. The Stay should be however more that 15 Days. Parents will need to show proof that their son or daughter is a Canadian Citizen or PR and relationship proof. Please carry copy of Canadian Passport of your Son or Daughter OR copy of his/her PR Card and Indian Passport. Also carry copy of his/her birth certificate showing your name as parents. If your Canadian son/daughter has Indian OCI Card or Old Indian Cancelled Passport, you may carry copy of that also as these documents have parents name on last page. Additionally keep with you contact details of your son/daughter and plan he/she has made for you for your quarantine when you arrive in Canada. Wife/Husband going to meet Husband/Wife may keep Marriage Certificate as a proof of relationship.
Normally any Visitor Visa Holder is required to enter Canada with a return or onward ticket. At present this rule is relaxed for Parents and Children till normal flight operations begin. This question is not asked as per feed back of our customers who have traveled on one way ticket. Even if it is asked to you, you may say that return ticket is not available in India's National Carrier Air India.
Work Permit Holders, Students (Provided you have a written letter of University that physical presence of Student is required in Canada), Those having PR Approval, can also travel to Canada. They must please refer below official link.